Ambulatory medical apparatus and method using a telemetry system with predefined reception listening periods

ABSTRACT

An implanted medical device (e.g. infusion pump) and an external device communicate with one another via telemetry messages that are receivable only during windows or listening periods. Each listening period is open for a prescribed period of time and is spaced from successive listening periods by an interval. The prescribed period of time is typically kept small to minimize power consumption. To increase likelihood of successful communication, the window may be forced to an open state, by use of an attention signal, in anticipation of an incoming message. To further minimize power consumption, it is desirable to minimize use of extended attention signals, which is accomplished by the transmitter maintaining an estimate of listening period start times and attempting to send messages only during listening periods. In the communication device, the estimate is updated as a result of information obtained with the reception of each message from the medical device.

RELATED APPLICATIONS

This application claims the benefit of prior filed U.S. ProvisionalPatent Application No. 60/177,414; filed Jan. 21, 2000, by Ronald J.Lebel, et al., and entitled “Medical Apparatus and Method Including anImplantable Device and an External Communication Device”. The entiretyof this provisional application is hereby incorporated herein by thisreference, including appendices filed therewith and any referencesincorporated therein by reference, as if set forth in full herein.

FIELD OF THE DISCLOSURE

This invention relates generally to ambulatory medical systems thatinclude a medical device and a control device that communicate viatelemetry and that initiate message reception during predefinedlistening periods. Preferred embodiments relate to implantable infusionpumps and external devices for communicating therewith.

BACKGROUND

Various ambulatory medical devices have been proposed and a number ofsuch devices are commercially available. These devices include, forexample, implantable infusion pumps, externally carried infusion pumps,implantable pacemakers, implantable defibrillators, implantable neuralstimulators, implantable physiological sensors, externally carriedphysiologic sensors, and the like.

As appropriate operation of ambulatory medical devices may be criticalto those patients being treated using those devices, and as telemetrycommunications between ambulatory medical devices and controllers cangreatly enhance the convenience of using such devices, or even be anenabling necessity to the use of such devices (e.g. implantable deviceswith sophisticated functionality), the operation of such medical devicescan benefit significantly by use of telemetry systems and protocols thathave features/elements that lead to optimization of various attributes.Such attributes may include (1) flexibility in communicating the widevariety signals that may be useful to controlling and retrievinginformation from a sophisticated medical device, (2) robustness indistinguishing actual signals from noise, (3) robustness indistinguishing valid signals from corrupt signals, (4) robustness inascertaining when appropriate communication has occurred and whenadditional communication must be attempted, (5) a reasonable efficiencyin communication time, and/or (6) a reasonable efficiency in electricalpower consumption associated with conveying information over thetelemetry system.

Implantable medical devices typically operate by battery power. Thebatteries may or may not be rechargeable. Higher consumption of powerfrom an implantable medical device containing non-rechargeable batteriesleads to a shortening of the usable life of the device and an associatedincreased frequency of surgery, potential pain, recovery, andinconvenience. Higher consumption of power from an implantable medicaldevice containing rechargeable batteries leads to more frequent chargingperiods for the batteries and associated inconvenience and may lead toan overall shortening of the usable life of the device. As such, whetheror not an implantable medical device contains rechargeable batteries ornon-rechargeable batteries, it is desirable to lower the powerconsumption of the device. As telemetry reception and transmission arehighly energy consumptive, it is desirable to minimize the operationtime of telemetry reception and transmission modules.

A telemetry reception module of a first device needs to (1) be poweredto listen for potential incoming messages from a second device, (2) staypowered during the entire receipt of the message, and (3) potentially bepowered one or more repeated times to receive a duplicate message whenthe second device is expecting a response to its original message anddoes not receive one. A telemetry transmission module of a first deviceneeds to (1) be powered so it can transmit a desired message to a seconddevice, and (2) potentially be powered one or more times to retransmit aduplicate message when the first device fails to receive confirmationthat original message was received by the second device.

A need exists in the field for improved telemetry features/elements thattend to minimize one or both of power on time for telemetry receptionmodules and/or telemetry transmission modules to reduce power drain onbatteries used in powering ambulatory medical devices and communicators.A need exists in the field to ensure that device users are notinconvenienced with long delay times that may be associated withinputting information into the communication device, transmittinginformation via telemetry to the medical device, and waiting forconfirmation that the transmitted information was appropriately receivedand is was or will be appropriately acted upon.

SUMMARY OF THE INVENTION

It is a first object of certain aspects of the invention to reduce powerconsumption in an ambulatory medical system associated with receivingmessages via telemetry.

It is a second object of certain aspects of the invention to reducepower consumption in an ambulatory medical system associated withtransmitting messages via telemetry.

It is a third object of certain aspects of the invention to shift powerconsumption burdens associated with telemetry activities away from animplantable medical device to an external communication device.

It is a fourth object of certain aspects of the invention to achieveenhanced synchronization between timers in the medical device and in thecommunication device than is inherently achieved based on frequencyoscillation tolerance differences allowed in the principle oscillatorsused in the two devices.

Other objects and advantages of various aspects of the invention will beapparent to those of skill in the art upon review of the teachingsherein. The various aspects of the invention set forth below as well asother aspects of the invention not specifically set forth below butascertained from the teachings found herein, may address the above notedobjects or other objects ascertained from the teachings hereinindividually or in various combinations. As such, it is intended thateach aspect of the invention address at least one of the above notedobjects or address some other object that will be apparent to one ofskill in the art from a review of the teachings herein. It is notintended that all, or even a portion of these objects, necessarily beaddressed by any single aspect of the invention even though that may bethe case with regard to some aspects.

It is a first aspect of the invention to provide a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein the CD telemetry system listensduring preselected outbound listening periods for at least a selectedtype of message from the MD telemetry system.

In a specific variation of the first aspect of the invention, themedical device is capable of initiating communication with thecommunication during outbound listening periods, and the communicationdevice additionally includes (a) a CD clock system; (b) CD monitoringsystem that monitors a CD time, based on the CD clock system, thatcorresponds to a selected portion of a message received by the CDtelemetry system from the MD telemetry system; and (c) a CD controlsystem for effectively comparing the CD time to an anticipated outboundtransmission start time by the MD telemetry system for that selectedportion of the message to adaptively adjust a subsequent outboundlistening period based, at least in part, on the comparison of the CDtime to the anticipated outbound transmission start time.

In another variation of the first aspect of the invention, the MDtelemetry system activates a window for receiving messages from the CDtelemetry system during prescribed inbound listening periods and whereinsuccessive prescribed inbound listening periods are separated by asmaller interval than an interval that separates successive outboundlistening periods.

A second aspect of the invention provides a medical system that includes(a) an ambulatory medical device (MD) that includes MD electroniccontrol circuitry that further includes at least one MD telemetry systemand at least one MD processor that controls, at least in part, operationof the MD telemetry system and operation of the medical device, whereinthe medical device is configured to provide a treatment to a body of apatient or to monitor a selected state of the body; and (b) acommunication device (CD) that includes CD electronic control circuitrythat further includes at least one CD telemetry system and at least oneCD processor that controls, at least in part, operation of the CDtelemetry system and operation of the communication device, wherein theCD telemetry system sends messages to or receives messages from the MDtelemetry system, wherein the CD telemetry system does not send out amessage as the message is generated but instead delays the sending outof a message until a next prescribed inbound transmission start timeoccurs.

A third aspect of the invention provides a medical system that includes(a) an ambulatory medical device (MD) that includes MD electroniccontrol circuitry that further includes at least one MD telemetry systemand at least one MD processor that controls, at least in part, operationof the MD telemetry system and operation of the medical device, whereinthe medical device is configured to provide a treatment to a body of apatient or to monitor a selected state of the body; and (b) acommunication device (CD) that includes CD electronic control circuitrythat further includes at least one CD telemetry system and at least oneCD processor that controls, at least in part, operation of the CDtelemetry system and operation of the communication device, wherein theCD telemetry system sends messages to or receives messages from the MDtelemetry system, wherein the MD telemetry system listens for anymessages coming from the CD telemetry system beginning at prescribedinbound listening start times for prescribed inbound listening periods.

In a specific variation of the third aspect of the invention, thecommunication device attempts to anticipate the prescribed inboundlistening periods and sets inbound transmission start times tocorrespond to the anticipated prescribed inbound listening periods.

In another specific variation of the third aspect of the invention, theprescribed inbound listening start times and prescribed inboundlistening periods are determined and activated automatically withoutmicroprocessor intervention.

A fourth aspect of the invention provides a medical system that includes(a) an ambulatory medical device (MD) that includes MD electroniccontrol circuitry that further includes at least one MD telemetry systemand at least one MD processor that controls, at least in part, operationof the MD telemetry system and operation of the medical device, whereinthe medical device is configured to provide a treatment to a body of apatient or to monitor a selected state of the body; and (b) acommunication device (CD) that includes CD electronic control circuitrythat further includes at least one CD telemetry system and at least oneCD processor that controls, at least in part, operation of the CDtelemetry system and operation of the communication device, wherein theCD telemetry system sends messages to or receives messages from the MDtelemetry system, wherein the MD telemetry system and the CD telemetrysend and receive messages using digital modulation and demodulation.

In a specific variation of the eleventh aspect of the invention thedigital modulation and demodulation uses spread spectrum technology.

In another specific variation of the eleventh aspect of the invention,the MD telemetry system includes (1) a digital modulator, (2) areceiving amplifier, (3) a digital receiver, (4) a mixer, and (5) a lowpass filter wherein at least two of (1)-(5) are combined into a singleintegrated circuit or where all of (1)-(5) are combined into no morethan two integrated circuits.

A fifth aspect of the invention provides a medical system that includes(a) an ambulatory medical device (MD) that includes MD electroniccontrol circuitry that further includes at least one MD telemetry systemand at least one MD processor that controls, at least in part, operationof the MD telemetry system and operation of the medical device, whereinthe medical device is configured to provide a treatment to a body of apatient or to monitor a selected state of the body; and (b) acommunication device (CD) that includes CD electronic control circuitrythat further includes at least one CD telemetry system and at least oneCD processor that controls, at least in part, operation of the CDtelemetry system and operation of the communication device, wherein theCD telemetry system sends messages to or receives messages from the MDtelemetry system, wherein at least one of the communication device orthe medical device sets a preamble length, for at least some messages,as a function of at least the difference between a present time and atime of a previous communication.

In a specific variation of the fifth aspect of the invention, theestimated listening time is based, at least in part, on a timedifference between the present time and a time of a previously receivedmessage. In a further variation, the communication device derives theestimate. In still a further variation a transmission time is based, atleast in part, on a predefined desired transmission time as modified byan estimated amount of drift that may have occurred between a time baseused by the medical device and a time base used by the communicationdevice

A sixth aspect of the invention provides a medical system that includes(a) an ambulatory medical device (MD) that includes MD electroniccontrol circuitry that further includes at least one MD telemetry systemand at least one MD processor that controls, at least in part, operationof the MD telemetry system and operation of the medical device, whereinthe medical device is configured to provide a treatment to a body of apatient or to monitor a selected state of the body; and (b) acommunication device (CD) that includes CD electronic control circuitrythat further includes at least one CD telemetry system and at least oneCD processor that controls, at least in part, operation of the CDtelemetry system and operation of the communication device, wherein theCD telemetry system sends messages to or receives messages from the MDtelemetry system, wherein at least one of the communication device orthe medical device determines an estimated listening time for the otherof the communication device or the medical device and sets atransmission start time as a function of the estimated listening time.

A seventh aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein the medical device or thecommunication device comprises an oscillator circuit that produces apulse stream that oscillates at an initial frequency that is greaterthan a desired frequency and wherein signals from the oscillator circuitare passed through circuitry that removes selected pulses from an inputpulse stream such that a modified oscillator signal is produced having amodified pulse stream that oscillates with an average frequency closerto a desired frequency than the initial frequency.

In a specific variation of the seventh aspect of the invention, thecircuitry comprises a counter that repetitively counts to a firstpredefined value and then removes a pulse from the initial pulse streamto produce the modified pulse stream. In a further variation, a timingsignal is generated from the modified pulse stream by utilization of acounter that counts to a second predefined value and then outputs apulse. In a further variation, the first predefined value is defined bysoftware. In still a further variation, the first predefined value issubject to modification during a normal course of operation of themedical system. In still a further variation, the modification of thefirst predefined value causes the modified pulse stream to oscillate ata frequency closer to the desired frequency than it otherwise would ifit remained unchanged. In still a further variation the modification ofthe first predefined value is at least in part based on a temperature ofthe oscillator circuit.

An eighth aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein at least one of the medical deviceor the communication device periodically adjusts a concept of time tomatch at least in part a concept of time in the other of thecommunication device or the medical device.

In a specific variation of the eighth aspect of the invention, theconcepts of time of the medical device and the communication device areused by each for controlling, at least in part, telemetry operations ofthe medical device and communication device, respectively.

In another specific variation of the eighth aspect of the invention, afirst of the communication device or the medical device adjusts a firstconcept of time to match that of the second of the communication deviceor medical device, while the second of the medical device or thecommunication device matches a second concept of time to that of thefirst of the communication device or medical device.

A ninth aspect of the invention provides a medical system that includes(a) an ambulatory medical device (MD) that includes MD electroniccontrol circuitry that further includes at least one MD telemetry systemand at least one MD processor that controls, at least in part, operationof the MD telemetry system and operation of the medical device, whereinthe medical device is configured to provide a treatment to a body of apatient or to monitor a selected state of the body; and (b) acommunication device (CD) that includes CD electronic control circuitrythat further includes at least one CD telemetry system and at least oneCD processor that controls, at least in part, operation of the CDtelemetry system and operation of the communication device, wherein theCD telemetry system sends messages to or receives messages from the MDtelemetry system, wherein the communication device further comprises aCD timing module, a CD crystal oscillator, and at least one CDtemperature transducer, and wherein the CD timing module uses at leastthe CD temperature transducer in combination with known properties ofthe CD crystal oscillator to modify a rate of tracking of time by the CDtiming module.

In a specific variation of the ninth aspect of the invention, hemodified time is used in transmitting messages to the medical device. Ina further variation, the medical device listens only part of the timefor incoming messages from the CD telemetry system or transmitsunsolicited messages to the communication device only at selected times,and the communication device estimates the medical device's inboundlistening times or potential outbound transmission times based, at leastin part, upon at least one temperature measurement made since a lastmessage was exchanged between the medical device and the communicationdevice in combination with known variations in crystal oscillationfrequency with temperature.

A tenth aspect of the invention provides a medical system that includes(a) an ambulatory medical device (MD) that includes MD electroniccontrol circuitry that further includes at least one MD telemetry systemand at least one MD processor that controls, at least in part, operationof the MD telemetry system and operation of the medical device, whereinthe medical device is configured to provide a treatment to a body of apatient or to monitor a selected state of the body; and (b) acommunication device (CD) that includes CD electronic control circuitrythat further includes at least one CD telemetry system and at least oneCD processor that controls, at least in part, operation of the CDtelemetry system and operation of the communication device, wherein theCD telemetry system sends messages to or receives messages from the MDtelemetry system, wherein the medical device further comprises an MDtiming module, an MD crystal oscillator, and at least one MD temperaturetransducer, and wherein the MD timing module uses at least the MDtemperature transducer in combination with known properties of the MDcrystal oscillator to modify a rate of tracking of time by the MD timingmodule.

An eleventh aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein the MD telemetry system isactivated to enable reception or transmission of messages only a portionof the time.

A twelfth aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein the medical device sends outunsolicited messages to the communication device.

A thirteenth aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein the medical device sends outboundmessages to the communication device and the communication devicereceives outbound messages from the medical device; wherein the medicaldevice receives inbound messages from the communication device and thecommunication device sends inbound messages to the medical device;wherein the medical device listens for inbound messages beginning at aninbound listening start time and continuing for an inbound listeningperiod; wherein the communication device listens for outbound messagesbeginning at an outbound listening start time and continuing for anoutbound listening period; wherein the medical device transmits outboundmessages beginning at an outbound transmission start time and continuestransmission of a selected portion of the outbound messages for anoutbound transmission period; wherein the communication device transmitsinbound messages beginning at an inbound transmission start time andcontinues transmission of a selected portion of the inbound messages foran inbound transmission period; wherein an interval exists betweensuccessive inbound listening periods; wherein an interval exists betweensuccessive outbound listening periods; and wherein at least a selectedone of (1) or (2) occurs: (1) at least one of the inbound transmissionperiod or the outbound transmission period is extended after a failureto communicate occurs; or (2) at least one of the inbound transmissionstart times or outbound transmission start times undergoes a shiftrelative to an anticipated inbound listening start time or ananticipated outbound listening start time, respectively; and whereinafter one or more extensions and/or one or more shifts, all portions ofthe interval between successive inbound or outbound listening periodswould be broadcast to during inbound transmission periods or outboundtransmission periods, respectively.

A fourteenth aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein at least one of the MD telemetrysystem or the CD telemetry system is configured to establish framesynchronization and to confirm that a message is intended specificallyfor the medical device or the communication device, respectively, byconfirming receipt of a predefined identifier.

A fifteenth aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein a timing associated with atransmission of a message or reception of a message, by one of themedical device or the communication device is based, at least in part,on an estimate of the amount of drift in time that has occurred betweena present time and a time of a previous synchronization of a timer inthe medical device and a timer in the communication device.

A sixteenth aspect of the invention provides a medical system thatincludes (a) an ambulatory medical device (MD) that includes MDelectronic control circuitry that further includes at least one MDtelemetry system and at least one MD processor that controls, at leastin part, operation of the MD telemetry system and operation of themedical device, wherein the medical device is configured to provide atreatment to a body of a patient or to monitor a selected state of thebody; and (b) a communication device (CD) that includes CD electroniccontrol circuitry that further includes at least one CD telemetry systemand at least one CD processor that controls, at least in part, operationof the CD telemetry system and operation of the communication device,wherein the CD telemetry system sends messages to or receives messagesfrom the MD telemetry system, wherein the MD telemetry system does notsend out a message as the message is generated but instead delays thesending out of a message until a next prescribed outbound transmissionstart time occurs.

Additional specific variations, provide the medical devices of each ofthe above aspects and above noted variations as implantable devices suchas implantable infusion pumps, implantable physiological sensors,implantable stimulators, and the like, or external devices suchsubcutaneous delivery infusion pumps or sensors that ascertain aphysiological parameter or parameters from subcutaneous tissue or fromthe skin of the patient. Such infusion pumps may dispense insulin,analgesics, neurological drugs, drugs for treating AIDS, drugs fortreating chronic ailments or acute ailments. Sensors may be used todetect various physiological parameters such as hormone levels, insulin,pH, oxygen, other blood chemical constituent levels, and the like. Thesensor may be of the electrochemical type, optical type, and may or maynot be enzymatic in operation.

In even further variations of the above noted aspects, and above notedvariations, one or more of the following is provided: (1) a firstportion of the MD telemetry system is incorporated into the MD processorand a second portion of the MD telemetry system is external to the MDprocessor, (2) a first portion of the CD telemetry system isincorporated into the CD processor and a second portion of the CDtelemetry system is external to the CD processor, (3) the MD processorincludes an MD central processing unit and at least one other MDfunctional module, (4) the CD processor includes a CD central processingunit and at least one other CD functional module, (5) the MD electroniccontrol circuitry includes at least one external MD functional module,other than a portion of the MD telemetry system, that is external to theMD processor, or (6) the CD electronic control circuitry includes atleast one external CD functional module, other than a portion of the CDtelemetry system, that is external to the CD processor.

Still additional aspects of the invention provide method counterparts tothe above system aspects as well as to other functional associations andrelationships, and processes that have not been specifically set forthabove but will be understood by those of skill in the art from a reviewof the teachings provided herein.

Further aspects of the invention will be understood by those of skill inthe art upon reviewing the teachings herein. These other aspects of theinvention may provide various combinations of the aspects presentedabove as well as provide other configurations, structures, functionalrelationships, and processes that have not been specifically set forthabove.

BRIEF DESCRIPTION OF THE DRAWINGS

The above referred to objects and aspects of the present invention willbe further understood from a review of the description to follow, theaccompanying drawings, and the claims set forth hereafter, wherein:

FIG. 1a depicts a perspective view of the main body of the implantabledevice of the first preferred embodiment;

FIG. 1b depicts a perspective view of the support and catheter assemblythat attaches to the main body of the implantable device of the firstpreferred embodiment;

FIG. 2 depicts a perspective view of the external communication deviceof the first preferred embodiment;

FIG. 3 depicts a block diagram of the main components/modules of boththe implantable device and the external communication device of thefirst preferred embodiment;

FIG. 4a depicts a block diagram of components that may be used in apulse stealing device as is used by both the implantable device and theexternal communication device of the first preferred embodiment;

FIG. 4b depicts an example of the differences between a pulse stolenchain and a non-pulse stolen chain; and

FIG. 5 depicts a block diagram of a time synchronization module that isused in the first preferred embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Various details about the structural and functional configuration andoperation of preferred ambulatory medical devices and preferredcommunication devices are found in several U.S. patent applicationsfield concurrently herewith and incorporated herein by reference intheir entireties: (1) U.S. Ser. No. 09/768,045, (2) U.S. Ser. No.09/768,202, (3) U.S. Ser. No. 09/768,198, (4) U.S. Ser. No. 09/768,207,and (5) U.S. Ser. No. 09/768,221.

U.S. patent application Ser. No. 09/768,045, filed on Jan. 22, 2001(concurrently herewith), by Starkweather, et al., entitled “AmbulatoryMedical Apparatus and Method Having Telemetry Modifiable ControlSoftware”, corresponding to Medical Research Group, Inc. Docket No.USP-1075-A is hereby incorporated herein by this reference as if setforth in fill herein. This application provides teachings concerning animplantable medical device (e.g. infusion pump) and handheldcommunication device wherein the implantable device is capable ofoperating under control of different software programs, wherein a firstprogram operates after resetting the implantable device and is notcapable of allowing significant medical functionality but is capable ofselected telemetry operations including telemetry operations that allowreplacement software to be downloaded, and wherein a second program maybe caused to take control of the device and enables medicalfunctionality and selected telemetry operations but is incapable ofreceiving replacement software. It is also taught that a software imagemay be received in multiple messages where each message is provided withits own validation code and wherein a validation code for the wholeimage is provided and wherein each provided validation code mustcompared to a derived validation code prior to accepting the validity ofthe replacement software.

U.S. patent application Ser. No. 09/768,202, filed on Jan. 22, 2001(concurrently herewith), by Lebel, et at, entitled “Ambulatory MedicalApparatus and Method Using a Robust Communication Protocol”,corresponding to Medical Research Group, Inc. Docket No. USP-1076-A, ishereby incorporated herein by the references as if set forth in fullherein. An implanted medical device (e.g. infusion pump) and externaldevice communicate with one another via telemetry wherein messages aretransmitted under a robust communication protocol. The communicationprotocol gives enhanced assurance concerning the integrity of messagesthat impact medical operations of the implantable device. Messages aretransmitted using a multipart format that includes a preamble, a framesync, a telemetry ID, data, and a validation code. The data portion ofthe message includes an op-code that dictates various other elementsthat form part of the message. The data portion may also includeadditional elements such as sequence numbers, bolus numbers, andduplicate data elements. A telemetry ID for the transmitting device maybe implicitly embedded in the message as part of the validation codethat is sent with the message and that must be pre-known by the receiverto confirm the integrity of the received message.

U.S. patent application Ser. No. 09/768,198, filed on Jan. 22, 2001(coneurrently herewith), by Lebel, et al., entitled “Ambulatory MedicalApparatus with Hand Held Communication Device”, corresponding to MedicalResearch Group, Inc. Docket No. USP-1078-A, is hereby incorporatedherein by this reference as if set forth in full herein. Thisapplication provides teachings concerning an implantable medical device(e.g. infusion pump) and handheld communication device (CD) thatexchange messages via telemetry such that commands are supplied to theimplantable device and operational information is obtained therefrom.The CD is controlled, at least in part, by a processor IC according to asoftware program operating therein and provides feedback to a user via avisual display, an audio alarm, and a vibrational sierra, and allowsinput from the user via a touch sensitive keypad. Certain inputfunctions are restricted by password. The visual display includes anicon and fixed element display region and a bitmap display region. Thefixed element display region includes time and date displays, batteryand drug level displays that decrement, and a moving delivery statedisplay. Various screens allow operation or log information to bedisplayed and/or user entry of commands. Program features when disabledare removed from a series of screen options that can be scrolledthrough.

U.S. patent application Ser. No. 09/768,207, flied on Jan. 22, 2001(concurrently herewith), by Starkweather, et at, entitled “Method andApparatus for Communicating Between an Ambulatory Medical Device andControl Device Via Telemetry Using Randomized Data”, corresponding toMedical Research Group, Inc. Docket No. USP-1079-A, is herebyincorporated herein by this reference as if set forth in full herein.This application provides teachings concerning an implantable medicaldevice (e.g, infusion pump) and handheld communication device thatcommunicate with one another via telemetry wherein transmitted messageshave enhanced numbers of and/or regularity of bit transitions tominimize the risk of synchronization loss between transmitted bits ofdata and received bits of data. It is taught that bit transitions forportions of messages may be enhanced by applying a pseudo-randomizationscheme to those portions of messages that are transmitted in a way thatallows the receiver to extract the original data from the receivedrandomized data. Preferred randomization techniques modify (i.e.randomize) the data using a CRC value that is being accumulated whilesimultaneously causing the modified data to modify subsequentaccumulation of the CRC itself Upon reception, the reversal of datarandomization is then made to occur so that the intended message isappropriately received.

U.S. patent application Ser. No. 09/768,221, filed on Jan. 22, 2001(concurrently herewith), by Lebel, et al., entitled “MicroprocessorControlled Ambulatory Medical Apparatus with Hand Held CommunicationDevice”, corresponding to Medical Research Group, Inc. Docket No.USP-1080-A, is hereby incorporated herein by this reference as if setforth in full herein. This application provides teachings concerning animplantable medical device (e.g. infusion pump) and handheldcommunication device, wherein an implantable infusion pump possessesoperational functionality that is, at least in part, controlled bysoftware operating in two processor ICs which are configured to performsome different and some duplicate functions. The pump exchanges messageswith the external communication device via telemetry. Each processorcontrols a different part of the drug infusion mechanism such that bothprocessors must agree on the appropriateness of drug delivery forinfusion to occur. Delivery accumulators are incremented and decrementedwith delivery requests and with deliveries made. When accumulatedamounts reach or exceed, quantized deliverable amounts, infusion is madeto occur. The accumulators are capable of being incremented by two ormore independent types of delivery requests. Operational modes of theinfusion device are changed automatically in view of various systemerrors that are trapped, various system alarm conditions that aredetected, and when excess periods of time lapse between pump andexternal device interactions.

The first embodiment of the present invention provides a long termimplantable medical delivery system that controllably supplies insulinto the body of a patient afflicted with diabetes mellitus. Thisembodiment includes an implantable medical device and an externalcommunication device. In the most preferred embodiments, thecommunication device is a hand held device that is used directly by thepatient to interact with the medical device as opposed to being limitedto use by a physician, nurse, or technician. It is preferred that thecommunication device provide (1) the ability to send commands to themedical device, (2) receive information from the medical device, and (3)be able to present to the patient at least a portion of the informationit receives from the medical device. In preferred embodiments, thepatient interacts with the medical device via the communication deviceat least once per week, on average, more preferably at least once everyother day, on average, and most preferably at least once per day, onaverage.

The implantable medical device (MD) includes a biocompatible housing; areservoir within the housing for holding a quantity of insulin; a sideport that attaches to the side of the housing, a catheter, that connectsto the side port; a pumping mechanism, within the housing for moving theinsulin from the reservoir through the sideport and through the catheterto the body of the patient; and control, monitoring, and communicationelectronics located within the housing. In alternative embodimentsvarious portions of implantable medical device hardware may be locatedoutside the housing. For example, the pumping mechanism or a telemetryantenna may be located within the sideport or other side mountedhousing; or a telemetry antenna may mounted on the outside surface ofthe housing, or extend along the catheter

The external communication device (CD) communicates commands to themedical device, receives information from the medical device, andcommunicates system status and system history to the patient. Theexternal communication device includes a housing; a keypad mounted onthe housing; a display forming part of the housing; and control,monitoring, and communication electronics located within the housing. Inalternative embodiments, the keypad may be replaced in whole or in partby a touch sensitive display or a voice recognition system. In addition,or alternatively, the display may be replaced in whole or in part by aspeech generation system or other audio communication system.

The outer appearance of the implantable device 2 is depicted in twopieces in FIGS. 1a and 1 b and includes housing 6 having a drug outletport 8, and a refill port 12, a removable sideport 14 that mountsagainst the side of the housing 6 over outlet port 8, and a catheter 16having a distal end 18 and a proximal end that attaches to sideport 14.In alternative embodiments, the implantable device may take on adifferent shape and/or the sideport may be removed in favor of apermanently mounted catheter assembly.

The outer appearance of the external communication device 32 is depictedin FIG. 2. The various components of the external communication deviceare fitted in or on housing 34. Housing 34 is divided into a frontportion 34 a and a back portion 34 b. The front portion 34 a is providedwith an opening in which an LCD panel 36 is positioned. The panel 36 hasa lower portion that is a bit map display and an upper portion thatprovides icons and fixed element displays. The front portion 34 a of theexternal communication device is also provided with a five-elementkeypad 38. A first key 38 a is not located under a raised pad and doesnot provide tactile feedback when it is touched and may be used forspecial functions. The remaining four keys 38 b, 38 c, 38 d, and 38 ehave raised pads that provide tactile feedback when they are depressed.These remaining keys may be used in normal device operation and areknown as the select key, the up arrow key, down arrow key, and theactivate key, respectively. The back portion 34 b of the housing isfitted with a door under which a compartment is located for holding areplaceable battery.

FIG. 3 depicts a simplified block diagram of various functionalcomponents or modules (i.e. single components or groups of components)included in the implantable medical device 2 and external communicationdevice 32. The external communication device 32 includes (1) a housingor cover 34 preferably formed from a durable plastic material, (2)processing electronics 42 including a CPU and memory elements forstoring control programs and operation data, (3) an LCD display 36 forproviding operation for information to the user, (4) a keypad 38 fortaking input from the user, (5) an audio alarm 44 for providinginformation to the user, (6) a vibrator 46 for providing information tothe user, (7) a main battery 52 for supplying power to the device, (8) abackup battery 54 to provide memory maintenance for the device, (9) aradio frequency (RF) telemetry system 56 for sending signals to theimplantable medical device and for receiving signals from theimplantable medical device, and (10) an infrared (IR) input/outputsystem 58 for communicating with a second external device.

The second external device may include input, display and programmingcapabilities. The second device may include a personal computeroperating specialized software. The computer may be used to manipulatethe data retrieved from the communication device or the medical deviceor it may be used to program new parameters into the communicationdevice or directly into the medical device, or even used to download newsoftware to the communication device or to the medical device. Themanipulation of the data may be used in generating graphical displays ofthe data to help aid in the interpretation of the data. Such datainterpretation might be particularly useful if the medical deviceprovides data concerning a physiological parameter of the body of thepatient, such as a glucose level versus time. More particularly thecomputing power and display attributes of the second device might beeven more useful when the medical device includes both an implantedsensor (e.g. glucose sensor), or external sensor, and an implanted pump(e.g. insulin pump), or external pump, where the second external devicemay be used to enhance the ability to ascertain the effectiveness of thetwo devices working together. Successful control periods and problemcontrol periods could be more readily identified. In fact, if the twodevices work on a closed loop basis or semi-closed loop basis, theanalysis performable by the second external device may be useful inderiving new closed loop control parameters and/or in programming thoseparameters directly into the communication device or the medical deviceor devices.

The implantable device 2 includes (1) a housing or cover 6 preferablymade of titanium that may or may not be coated to enhancebiocompatibility, (2) processing electronics 72 including two CPUs andmemory elements for storing control programs and operation data, (3)battery 74 for providing power to the system, (4) RF telemetry system 76for sending communication signals (i.e. messages) to the external deviceand for receiving communication signals (i.e. messages) from theexternal device, (5) alarm or buzzer 82 for providing feedback to theuser, (6) refill port 12 for accepting a new supply of drug as needed,(7) reservoir 84 for storing a drug for future infusion, (8) pumpingmechanism 86 for forcing selected quantities of drug from the reservoirthrough the catheter to the body of the patient, (9) sideport 14 forproviding a replaceable connection between the (10) catheter and thepump housing and for allowing diagnostic testing of the fluid handlingsystem to occur, and catheter 16 for carrying medication from theimplant location to the desired infusion location.

In this embodiment, the pump mechanism is preferably a low power,electromagnetically driven piston pump. Such as for example Model Nos.P650005 or P650009 as sold by Wilson Greatbatch Ltd. of Clarence, N.Y.which have stroke volumes of 0.5 microliters and draw under 7 mJ (e.g.about 6 mJ) per pump stroke and under 4 mJ (e.g. about 3 mJ) per pumpstroke, respectively. The pump mechanism dispenses a sufficiently smallvolume of insulin per stroke so that a desired level of infusionresolution is achieved. For example if an infusion resolution of 0.2units of insulin were desired when using U400 insulin, then a strokevolume of about 0.5 microliters would be appropriate. In otherembodiments other types of infusion pumps may be used, e.g. peristalticpumps.

The size of the reservoir is preferably large enough to hold sufficientinsulin so that refilling does not have to occur too often. For example,it is preferred that time between refills be within the range of 1.5-4months or longer, more preferably at least 2 months, and most preferablyat least 3 months. Opposing the containment of a large volume ofinsulin, is the desire to keep the implantable device as small aspossible. In the present embodiment the implantable device and reservoirhas been designed to hold about 13 ml of insulin. A preferred insulinhas a concentration of 400 units per milliliter and is available fromAventis HOE 21Ph U-400 from Aventis Pharma (formerly Hoechst MarionRoussel AG, of Frankfurt am Main, Germany). This insulin is a highlypurified, semi-synthetic human insulin with 0.2% phenol as a preservingagent, glycerol as an isotonic component, TRIS as a buffer, plus zincand Genopal® as stabilizing agents. This quantity and insulinconcentration allows about 2-4 months between refills. In otherembodiments higher insulin concentrations may be used (e.g. U-500 orU-1000) to increase time between refills or to allow reduction inreservoir size. In some embodiments, when higher concentrations areused, any quantized minimum delivery amounts may be reduced by modifyingthe pumping mechanism, control circuitry, or software control algorithmso that infusion resolution is not adversely impacted.

The external communication device contains appropriate software toprovide proper control of the device including appropriate functionalityto allow communication with the medical device, to allow adequatecontrol of the operation of the medical device, and to give appropriatefeedback to the user regarding overall system operation. The medicaldevice is provided with appropriate software to allow communication withthe external communication device, to allow safe and appropriateoperation of the medical functionality of the device, and to allowdirect feedback to the user concerning device status via the internalalarm.

The control electronics of both the implantable device and externalcommunication device are centered around microprocessor based integratedcircuits, i.e. processor ICs, that are implemented in the presentembodiment in the form of application specific integrated circuits(ASICs). In the present embodiment, the control electronics of theimplantable device are centered around two identical ASICs that aremounted on a hybrid circuit board. Two such ASICs are used in theimplantable device to increase operational safety of the device byconfiguring the device to require that the two ASICs act in conjunctionwith each other in order for medication infusion to occur. In somealternative embodiments a single ASIC may be used, or a single dualprocessor integrated ASIC may be used. In a single processor device oneor more circuits may be provided to monitor the operation of a CPU inthe processor to ensure it continues to operate properly in one or morekey functions. In the single dual processor integrated ASIC, dualcircuitry would be provided so that each processor could actindependently of the other. In the single dual processor embodiment, asingle off-circuit oscillator may be used to drive both processors oreach may have an independent oscillator. A single chain of timingcircuits could be used in driving both processors or independent chainsof timing circuits could be used. Furthermore, if a single oscillator isused to drive both processors, then one or more separate circuits suchas a counter and an RC timer may be used to verify appropriate operationof the oscillator and/or any particular timing circuit dependentthereon.

In different embodiments, more or less of the control electronics may beimplemented within one or more processor ICs while any remainingportions may be implemented external to the processor IC(s). Theprocessor IC may be referred to as an MD processor if used in themedical device portion of the system or a CD processor if used in thecommunication device portion of the system. In other embodiments theprocess IC used in the communication device may be different, e.g. havea different CPU or different peripheral modules, from a processor ICused in the medical device. In embodiments where more than one processorIC is used in either the medical device or the communication device eachof the processors may be different. They may be specifically designedfor their intended roles when they perform at least partially differentfunctions. Depending on particular design constraints portions of theelectronics not embodied in the processor ICs may form part of one ormore hybrid circuit boards or be otherwise mounted within, on, or evenin some cases external to a device housing.

Each processor IC of the present embodiment includes a 16-bit core CPUwhich is a CMOS low power version of the INTEL 8086 processor andvarious peripheral modules that are used for system control, dataacquisition, and interfacing with electrical components external to theprocessor IC. The peripheral modules of the processor IC of the presentembodiment include (1) a non-volatile memory interface module, e.g. aSEEPROM interface module, (2) a boot ROM module; (3) an SRAM module; (4)a memory decoder module; (5) a crystal oscillator module; (6) a timermodule; (7) a pump interface module; (8) a watchdog module; (9) an RFmodule; (10) an interrupt handler module; (12) an analog-to-digitalconverter module; (13) an LCD clock driver module; (14) an alarminterface module; and (15) first and second synchronous serial interfacemodules.

In alternative embodiments fewer, additional, or different peripheralmodules may be incorporated into the processor ICs. In one extreme theprocessor IC may simply incorporate a CPU with all other modules beingexternal thereto. In the other extreme almost all, if not all,electronic components may be incorporated into a single processor IC.Intermediate alternatives might incorporate a single additional moduleinto the processor IC (in addition to the CPU), others might incorporatemore than one, e.g. 4 or more, 8 or more, or the like. In still otheralternatives, the number of peripheral modules or components in anentire device may be considered and more than a certain percentage ofthem incorporated into one or more processor ICs, e.g. more than 50%,more than 75%, or even more than 90%.

The processor ICs are responsible for basic system management andcommunication of information between the implantable device and theexternal communication device through the RF telemetry link. Thetelemetry systems of the present embodiment are implemented in partthrough electrical hardware and in part through software controlled by aprocessor IC.

In the present embodiment, most of the required electrical modules forthe implantable device are integrated within the processor ICs. However,several are not. These additional modules include two independentcrystal oscillators (one for each ASIC); two non-volatile memory modules(one for each ASIC), e.g. SEEPROM chips; a volatile memory module (usedonly by one of the ASICs), e.g. an SRAM chip; pump driver circuitry(partially controlled by the each ASIC); front end telemetry systemcircuitry; and voltage measurement circuitry associated with the pumpdriver circuit; a buzzer; and a battery.

Within the implantable device telemetry operations are controlled by asingle ASIC (sometimes known as the main processor) The other processor(sometimes known as the monitor processor) controls the buzzer and isthus responsible for audio communications coming from the implantabledevice. The medical functionality of the implantable device (i.e. theadministration of insulin in the present embodiment) is controlled byboth processors. To maintain the implantable device in a fail safeoperational mode, these two processors maintain an appropriate level ofagreement concerning infusion instructions an error condition resultsand either pumping is halted or a system reset may be made to occur. Themain and monitor processors communicate with each other through the useof hardwired serial input and output ports.

As with the implantable device, the control electronics of the externalcommunication device are centered around an ASIC that controls andinteracts with a number of peripheral modules. These peripheral modulesinclude an LCD display and driver, an IR port and driver, a crystaloscillator, a keypad and keypad interface, power management modules andreset circuitry, external volatile memory (e.g. SRAM) and non-volatilememory (e.g. SEEPROM), a buzzer, and front end telemetry hardware.

Basic timing for each of the medical device and the communication deviceis provided by a low power crystal oscillator module within eachprocessor IC that is connected to an external crystal oscillator. In thepresent embodiment the crystal oscillators are configured to provide astable clock source of 1,049,100 MHz with a tolerance no greater than+/−500 parts per million (ppm) including drift due to aging, andvariation in oscillation due to temperature variations within a range of−10° to 50° C. This frequency and it tolerance are selected such thatthe lower extreme of the range is still slightly larger than a desiredfrequency (e.g. 1,048,576).

The clock source is used to drive a 20 bit system clock ripple counterthat is sometimes referred to as Counter B (CNT B). This ripple counteris used to provide system clocks of various frequencies for operation ofall other modules. Based on the above noted tolerance allowance on thecrystal oscillator frequency, drift in the concept of timing between themedical device and the communication device can be as large as about0.1% or about 3.6 seconds per hour. Though this level of drift may beacceptable for some purposes, it is not acceptable for others. Inparticular it is not acceptable for maintaining accurate time of daytracking over extended periods of time (e.g. 1 second shift per week)and it is even less acceptable for maintaining a level of timesynchronization between the two devices that allows optimized efficiencyof telemetry operations (e.g. 1 millisecond every 4 hours).

A pulse stealer circuit is provided for precise system timing ofselected clock signals. In the present embodiment the pulse stealerfunction is applied to the clock signal that has a frequency, asprovided by the system clock ripple counter, that is slightly more thanan 8192 Hz target frequency. The pulse stealer circuit gives the abilityto periodically steal single pulses from a selected clock signal toproduce a clock signal of lower average frequency. In the presentembodiment the modified signal, or pulse stolen signal, is used as thesource for the lower frequency clocks that are also generated by systemclock ripple counter. As some lower frequency non-pulse stolen clocksignals are desired for various uses in the system they are derived fromhigher frequency signals that are extracted from the ripple counterabove the pulse stolen levels. In implementing pulse stealing for thepresent embodiment, the CPU loads a 16 bit value into two eight bitconfiguration registers. The timer whose signal is to be modified isused to cause a counter to count up from zero to the value loaded intothe registers. After the counter reaches the value specified in theregisters, a single pulse is removed from the output signal (stolen fromthe output signal) to provide a modified output signal. Then thecounting begins again from zero and the process is repeated over andover so that a modified output signal, or pulse train, having a desiredaverage frequency is generated.

A value of 0×0000 loaded into these registers disables the pulse stealerand allows the approximately 8,192 Hz clock to pass though unmodified(i.e. input signal=output signal).

FIG. 4a, presents a block diagram showing the primary elements of apulse stealing circuit: (1) a crystal clock 242, (2) a divide circuit244, (3) a pulse stealing circuit 246, and (4) a timer circuit 248.

In the present embodiment the crystal clock 242 operates at a nominalfrequency of 1,049,100 Hz+/−500 Hz producing pulse train identified as“t1”. The divide circuit 244 in the present embodiment effectivelydivides by input frequency by a value X that is 128 and produces pulsetrain “t2” of nominal frequency 8196 Hz+/−3.9 Hz. The pulse stealingcircuit removes a single clock pulse repetitively from t2 to produce t3.The repetition rate is controlled by a programmed value set in the pulsestealing circuit. The repetition rate is set to an appropriate valuethat adjusts the input frequency (t2) to that desired by the timercircuit 248. In the present embodiment, it is desired that the pulsetrain t3 that feeds timer circuit 248 be precisely operating at 8192pulses/second.

The pulse stealing circuit includes a counter that runs off clock signalt2. The counter begins counting at zero and counts up to a value set inthe above noted configuration registers. When the counter reaches theprogrammed value, one clock pulse is removed from the signal t2 toproduce signal t3. The counter is reset to start the count again andcontinues in an endless loop.

FIG. 4b depicts a sample timing sequence for the input signal t2 andoutput signal t3 of the pulse stealing circuit where the register valueis set to five.

The timer circuit produces a pulse stream t3 having an effective averageclock frequency of,${\left( {1 - \frac{1}{{Value} + 1}} \right)*\left( {{Frequency}\quad {of}{\quad \quad}{t2}} \right)},$

where “value” is the value entered into the configuration registers.

The table presented below illustrates the effect of the pulse stealingregister value on the timer circuit clock.

12/21 Pulse Stealing Impact Timer Circuit Clock Frequency Value in the(t3) Relative to Input Configuration Registers Frequency (t2) 1 ½ 2 ⅔ 3¾ 4 ⅘ 5 ⅚

In the present embodiment, the pulse stealing circuit is designed toachieve an effective average timer circuit clock frequency of 8192 Hz.The required pulse stealing register value may be calculated from,${{DF} = {\left( {1 - \frac{1}{{Value} + 1}} \right)*{\left( {{crystal}\quad {frequency}} \right)/X}}},$

where DF is the desired frequency, and in the present embodiment is 8192Hz, and where X is the amount by which the crystal frequency is dividedprior to entering the pulse stealer, and in the present embodiment is128. This equation may be manipulated to yield,${{value} = {\frac{{crystal}\quad {frequency}}{{{crystal}\quad {frequency}} - 1048576} - 1}},$

where the value used for X was 128.

The table below illustrates some example register values based onexample crystal frequency values.

Sample Register Values Table Crystal Frequency Hz Register Value1,048,576 Cannot calculate = 0 1,048,700 8456 1,048,900 3236 1,049,1002001 1,049,300 1448 1,049,500 1134 1,049,624 1000

If, for example, the crystal frequency was measured to be 1,049,039 Hz.The calculated register value is 2264.74. However, since in the presentembodiment the counter only accommodates integer register values, theregister value will be set to either 2265 or possibly 2264. As a result,by use of this register value, the average frequency of signal t3 willbe brought as close as possible to the desired value.

A sample pulse stealing circuit for the present embodiment that uses upto a 16 bit pulse stealing value might include a 16 bit register, a 16bit counter, a 16 bit compare logic block, and a logic gate such as an“and” gate that takes two inputs, t2 and a normally high signal that istoggled low when the counter reaches the register value and then isreasserted high when the counting starts over. The compare logic blockmay be used to compare the value in the register to the value in thecounter to determine if the two are equivalent. The compare logic blockmay be based, for example, on 16 two-input AND gates whose outputs arefed into one or more additional AND gates to produce a single outputsignal indicative of whether the count has been met. As required,additional logic could be added as necessary, to interpret a 0000hregister value as disabling the pulse stealer.

Of course, in other embodiments the pulse stealing circuit may be drivenby a different signal t2 frequency or it may be driven directly from thecrystal clock. It may be made to steal more than one consecutive pulse.A different register size may be used. The signals generated by thepulse stealer may be used either directly by a circuit that is tolerantto a missing pulse or it may alternatively be used to drive one or moreadditional counters, or “divide by” circuits, wherein with eachsubsequent reduction in frequency, the uniformity of the final pulsetrain is improved as well as any difference between the modifiedfrequency and the desired frequency.

In other alternative embodiments, pulse stealing circuits may beindependently used on multiple modules or they may be stacked in seriesto provide an even more accurate average signal pulse frequency. Theregister value may be set once and then let alone or alternatively, itmay be changed periodically based on a defined criteria. For example, ifa given crystal oscillator circuit is known to vary its oscillationfrequency with temperature, or other parameter, the parameter may bemeasured and a revised value determined. The revised value may bedetermined by use of a look up table, calculation, or the like and theninserted into the register or otherwise used to institute pulsestealing.

As another example, if an increment in time as registered by a secondclock were compared to the same increment of time as measured by a firstclock, a drift rate or amount could be derived. The drift rate or amountcould then be used to calculate a revised pulse stealing value oradditional pulse stealing value for one or both of the clocks so as tomore closely synchronize their operation.

As further example, if the count value entered in the registers is notprecisely the desired value, the value entered into the register may beperiodically varied so that the average value in the register is closerto the desired value. As such, in one implementation the values enteredinto the register may alternate between the two values that bound eachside of the desired value. The proportion of the time that each of thebounding values is used may be based on the proportions of thedifferences between the desired value and each of the two boundingvalues. The period of time over which each value is used prior toswitching to the other value may vary depending on the amount of errorthat is allowed to build up. For example, the period may be smaller thanone minute or larger than one day. In other alternatives, otherimplementations are possible, for example where one of the alternativevalues used is something other than an immediately bounding value.

In the present embodiment telemetry reception and transmission timing byboth the medical device and the communication device are based on timeperiods that are derived from the pulse stolen clock signals. As thesepulse stolen clock signals have truer frequencies (on average) than dothe signals generated by the principle oscillator, the telemetry timingbetween the two devices will stay better synchronized. Furthermore asthe incrementing of the time of day clock in the communication device isalso is derived from the pulse stolen oscillator signals, the time ofday clock remains better synchronized to the actual time than itotherwise would have been. The pulse stolen clock signals are not usedfor driving circuits or functions that cannot tolerate missing pulses,e.g. pulse trains that are transmitting telemetry data.

The telemetry system for the implantable device and the externalcommunication device provide a half-duplex link between each other usinga carrier frequency of about 250 kHz (e.g. about 2{circumflex over ()}18 Hz) and a data signal having a frequency of about 8 kHz (e.g. about2{circumflex over ( )}13). The transmitter hardware uses an 8 kHz datasignal to modulate the carrier signal to generate signals that will betransmitted by the antenna. The receiver hardware receives the modulatedsignal and demodulates it to extract the 8 kHz data signal. Both theimplantable device and the external communication device have transmitand receive capabilities to allow two-way communication.

Most of the RF telemetry circuits necessary for communication betweenthe external communication device and the implantable device areimplemented in the processor IC. In order to minimize the digital noiseinterference that the processor IC might impart to the weak RF signalsthat are being received, a high-gain RF amplifier is implementedoff-chip. Also an RF antenna, that is used for both transmission andreception, and circuitry to select between reception and transmissionare implemented off-chip. The remaining analog sections and all thedigital demodulation circuits are implemented in the processor IC.

The RF module of the processor IC outputs in phase and quadrature phasesignal components for combined transmission by the external antenna. TheRF module also supplies a control signal that is used to switch betweena transmission configuration and a reception configuration. The RFmodule receives as inputs signals from the amplification circuitry.

A Quadrature Fast Acquisition Spread Spectrum Technique (QFAST®) is usedas the modulation technique. QFAST® modulation is based on an OffsetQuadrature Phase Shift Keying (QPSK) modulation technique. In thistechnique, data generated by the CPU modulates clock signals at thecarrier frequency. As a result of quadrature modulation, in-phase andquadrature-phase components of the given data stream are generated. Thetwo components are then applied to opposite ends of the external antennaso that a combined signal is transmitted.

The transmitter section of the telemetry system receives byte wideparallel data packets from the CPU and then loads the data into aparallel-to-serial shift register. The serial data is then sent to theQFAST® RF modulation transmitter section to modulate two quadratureclock signal components each operating with a carrier frequency of about2¹⁸ Hz) and shifted in phase relative to each other by 90 degrees. Thetwo components are then delivered to opposite ends of the antenna Aslong as there is data in the transmitter parallel-to-serial shiftregister, the RF transmitter remains activated. If the transmitterdoesn't have data available when the next byte is to be transmitted themessage is considered to have been completely transmitted and the CPUshuts off the transmitter circuitry so as to minimize continued powerdrain.

As noted above, external to the processor IC, the received RF signal isamplified by a high gain receive amplifier. A bandpass filter is used toattenuate out-of-band components such as those due to AM radio stations.The amplified RF signal then enters a mixer in the RF module of theprocessor IC and is converted to baseband using two mixers, one in-phasemixer and one quadrature phase mixer both at the carrier frequency. Themixer outputs are the quadrature components of the baseband signals. Anintegrator & dump function in the RF module then removes the sumfrequency (2 fc) and high frequency noise (i.e. acting as a low passfilter) from each of the two signals. The processed signals are thendigitized using a comparator and passed to the demodulator where thedata and clock are recovered.

In QFAST®, data rate adaptability is accomplished through aspread-spectrum “coding gain” concept, with the spreading code being asimple clock. The modulation produced by the QFAST® modulator isdemodulated in a manner which delivers both clock and data. All of theQFAST® modulation and demodulation circuits are digital and areincorporated into the processor IC.

The QFAST® technique provides a communication system with a number ofattributes: (1) it extracts the clock from the received signal without aclock recovery loop; (2) it provides demodulation of data without phaseambiguity and without the requirement for synchronous demodulation; (3)it makes effective use of the available transmission bandwidth, (4) itresults in fast acquisition of the message signal; (5) it is relativelyimmune to the effects of highly dispersive and distorting propagationmedia; (6) it does not require regeneration of a phase-coherent localreplica at the receiver of the transmitted carrier; (7) it does notrequire resolution of ambiguity between the in-phase andquadrature-phase channels in the receiver; and (8) it does not exhibitdata phase ambiguity.

Further detail about QFAST® (Quadrature Fast Acquisition Spread SpectrumTechnique) may be found in U.S. Pat. No. 5,559,828, entitled TransmittedReference Spread Spectrum Communication Using a Single Carrier with TwoMutually Orthogonal Modulated Basis Vectors, by Armstrong, et al.

The RF module in the processor IC consists of timing circuitry,circuitry to maintain time synchronization between the implantabledevice and the external communication device, a digital RF transmittersection that includes a QFAST® RF modulation transmitter, an analogreceive module, and a digital receive section that includes a QFAST® RFmodulation receiver.

The RF communication between the implantable device and the externalcommunication device occurs in the form of messages (sometimes referredto as communication signals or packets) that are passed back and forthbetween the two devices. In this embodiment these messages have amulti-part format or protocol: (1) preamble, (2) frame sync, (3)telemetry identifier, and (4) data.

In other embodiments other multipart formats may be used. For example,the multipart format might consist of (1) a preamble, (2) a telemetryidentifier, and (3) data. In still other embodiments the preamble andframe sync may be combined into a single entity, or the telemetryidentifier and the frame synch may be combined into a single entity, oreven all of the preamble, frame sync, and telemetry identifier may becombined into a single entity such that the functionality of associatedwith these individual elements of the messages of the present embodimentmay be performed simultaneously or in series based on a single butrepeated pattern of information.

For communications from the implantable device to the externalcommunication device the preamble is a repeating pattern of “10”, i.e.10101010. This alternating pattern of ones and zeros is broadcast for8-bit times. This pattern is considered the standard preamble pattern.In other embodiments this standard preamble pattern may be differentfrom that noted above (e.g. it may be a repeated pattern of “01” insteadof “10”). Though, unnecessary, the standard preamble need not transitionwith every other bit though, as a certain number of bit transitions aretypically necessary to establish bit synchronization, the moretransitions, the shorter the minimum length that the preamble can take.

For communications from the external communication device to theimplantable device, the preamble is either of the standard preamblepattern but applied for an extended number of bit times (e.g. 24, 48, or96) or is of an attention preamble pattern that is applied for,typically, even a longer extended number of bit times. In otherembodiments, not only may the preamble used by the implantable deviceand the external communication device have different lengths as used inthis embodiment, they may also use different standard preamble bitpatterns. Of course in still other embodiments, a same preamble lengthmay be used by both the implantable device and the externalcommunication device whether or not the same standard preamble bitpattern is used. The attention preamble pattern is formed of a repeatedpattern of “110110 . . . 110”. In other embodiments, other attentionpreamble patterns may be used (e.g. repetitions of “011”, “100”, “001,“1011”, and the like).

The preamble, whether of the standard pattern or the attention pattern,is used so that the RF reception hardware can establish bitsynchronization (i.e. bit boundary recognition) of the incoming data.However, the attention preamble is further used to get and hold thereceiver's attention for a defined period of time. As long as theattention preamble is being received, the receiver's hardware will stayon and continue tracking the signal in anticipation of an incomingmessage. In other embodiments, the concept of a standard preamblepattern that will not hold the receiver's attention may be dispensedwith in favor of always using a preamble that is in effect an attentionpreamble.

The attention preamble is considered to be lost, or no longer beingreceived, when the receiver receives more than 2 inappropriate bitvalues during receipt of any 64-bits or when the frame sync pattern isreceived.

Before beginning error detection, the receiver's hardware first requiresthat the receipt of the attention preamble be established. Inestablishing receipt of the attention preamble the receiver's hardwaremay load the received bits into a shift register and may then comparethe shifting pattern to a predefined pattern of selected length and thenmay consider the receipt of the attention preamble to be establishedonce the comparison indicates a match of sufficient length has occurred.The receive hardware then continues to compare received bits topredicted bits based on the pattern established. A bit counter isincremented with each bit received and an error counter is incrementedwith each error detected. The bit counter is reset whenever an error isdetected. The error counter is reset whenever the bit counter reach apreset value. If the error counter should reach a predefined erroramount, the established attention preamble is considered to have beenlost and if the receiver is still operating within its listening period,the receiver's hardware continues its process of trying to establishreceipt of attention preamble. The parameters associated withestablishing receipt of the attention preamble and associated with thesetting of error tolerances may be hardcoded into the system or they maybe programmable into hardware registers.

It is preferred that the above analysis be implemented in hardware dueto the energy saving possible but in other embodiments the process maybe implemented via software.

Of course in other embodiments, the error tolerance believed acceptablemay be increased or decreased or defined in a different manner. Forexample, instead of using an error tolerance of 2-bits out of 64-bits,one might use a tolerance of {fraction (1/32)}. The tolerance may evenbe increased to {fraction (2/32)}, {fraction (3/64)}, {fraction (4/64)},or even higher. Alternatively, it may be decreased to {fraction (1/64)},{fraction (1/128)} or even to zero.

The attention preamble may be used when there is some uncertainty in thetime synchronization of the two devices. The extra length of theattention preamble allows the receiver's reception window to open alittle later than anticipated and to still have the receiver pick up theentire message. The extra length of the attention preamble allows thereceiver's reception window to open earlier than anticipated, so long asa minimum number of bits are heard by the receiver during the time itsreception window is normally open, and still have the receiver'sattention locked onto the preamble and have the receiver remain on aslong as the attention preamble is being received, plus a little more, inanticipation of receiving a frame sync pattern.

The receiver may miss some of the initial bits in the preamble but aminimum number of bit transitions (e.g. 4, 6, or 8 transitions) of thepreamble pattern must be received to ensure bit synchronization betweenthe transmitted message and the receiver. In the present embodiment, theimplantable device broadcasts with a minimal preamble size in order toreduce power consumption within the implantable device. In otherembodiments, the preamble used by the implantable device may be largerrelative to the minimum number of bit transitions needed to establishbit synchronization.

In the present embodiment, frame sync may actually be considered bytesync (i.e. frames are bytes) and is a single byte of a selected patternand is used so the receiver can obtain byte boundaries for thetransmitted data. In the present embodiment, the selected pattern is“10110000”. In other embodiments, other patterns, pattern lengths, andframe sizes may also be acceptable for use as frame sync so long as thepatterns (in combination with preamble or attention preamble patternsand any tolerances in their reception) cannot lead to errors in definingbyte transitions. In still other embodiments, the attention preamblepattern may be of the same bit pattern as the frame sync, in which case,some error tolerance may be allowed in the frame sync pattern and thereceiver's attention would be held until the pattern is lost or a validtelemetry ID pattern is received.

Even during the receipt of attention preamble (or other preamble) thereceiver continually compares shifting bits that are received to theanticipated frame sync pattern. The Frame Sync byte may be detected byfeeding the incoming bit stream into a shift register and passing thebit values in the register to the inputs of an 8 input AND gate whoseinput assertion levels correspond to the anticipated frame sync pattern.

This comparison process continues so long as the receiver continues tolisten for an incoming message or until a valid frame sync pattern hasbeen received. If the receiver is continuing to listen beyond its normalreception window (i.e. listening period), due to the reception of anattention preamble, the listening will not stop immediately upon theattention preamble being lost. The comparison process for ascertainingthe receipt of frame sync continues for a number of bits after attentionpreamble is lost, even if the listening period has ended, as its lossmay be associated with the partial receipt of frame sync. Once framesync is received a valid frame sync signal is asserted.

In the present embodiment, the telemetry identifier (i.e. telemetry ID)is a 3-byte value that is used to ensure that only the intended receiverreceives a message. The value of all “1s” indicates a universal messagethat is to be received by all receivers, otherwise the telemetry ID mustbe agreed upon between the receiver and transmitter. A unique ID isprovided for each implantable device and each external communicationdevice during manufacturing. Only the external communication device cantransmit a message using the universal ID code. The telemetry IDs thatthe receiver will consider to be valid are the ID of the receiver or theuniversal ID. All other incoming bit patterns will be rejected with theresult that the receiver will be either turned off or will start againlooking for a valid frame sync pattern attention preamble. Inalternative embodiments, instead of the receiver accepting only its ownID (in addition to the universal ID) it may instead accept the ID of thetransmitter. In other alternative embodiments, a different lengthpreamble may be used by the implantable device and the externalcommunication device. In still further alternatives, the telemetry IDsmay not be unique if it is believed that the chance of miscommunicationbetween devices is not a significant risk. In fact, if there is littlerisk of miscommunication, telemetry ID may be dropped from the messageprotocol.

Other embodiments may retain the concept of telemetry ID for either thereceiver or the transmitter or both but only pass the telemetry IDinformation implicitly. Such implicit transfer might use the telemetryID information in generating a validation code (e.g. CRC) that istransferred with the message. In such cases the receiver could comparethe received code to one or more different codes generated using each ofthe unique telemetry ID and the universal telemetry ID. Theseembodiments would be less preferred when power consumptionconsiderations are critical, as the telemetry system of the receiverwould have to remain on to receive the entire message in order todetermine whether the message was for it or not.

After a Frame Sync byte is detected, the processor IC hardware comparesthe next 24 bits of the incoming data to the personal ID bits and to theuniversal ID which in this embodiment is fixed at 0×FFFFFF. Thedetection for the universal ID may be performed by passing the incomingdata stream (for these 24 bits) through an XOR gate along with anotherinput fixed at a value of 1. The output of the XOR gate may then be fedinto the data line of a D flip-flop while the clock line of theflip-flop is fed by a clock signal running at the bit rate. If the 24bits are processed without the output of flip-flop changing state avalid universal ID has been received. If the flip-flop does changestate, a universal failure signal is asserted. The incoming bits arealso passed through a first input of a second XOR gate while a secondinput of the gate is supplied by a multiplexer that provides bit valuesfrom the specific acceptable telemetry ID. The output of the XOR gate isprovided to a flip-flop in a manner analogous to that discussed abovefor detecting the universal ID. So long as the output of the flip-flopdoesn't change state during the processing of the 24 bits, a validspecific ID is considered to have been received, otherwise a specific IDfailure signal is generated. If and only if one of the ID failures isasserted, an ID valid signal is generated. If both ID failures aregenerated, the valid frame sync flag is de-asserted in which caselistening by the receiver may be aborted if the listening period hasexpired or listening for attention preamble and frame sync may continueif the listening period has not yet expired. If a valid telemetry ID isreceived, the receiver listens to the remaining portion of the message.

In alternative embodiments the frame sync and telemetry ID may becombined into a single entity that is identified as a whole as opposedto the present embodiment where the two pieces are looked for andidentified separately.

In the present embodiment, data is provided in an integer number ofbytes following the telemetry ID. In the present embodiment the firstbyte of the data indicates the message type. The first seven bits of thefirst byte is an operation code or op-code while the eighth bit iseither ignored or is set and interpreted as a sequence number (to bediscussed hereafter) dependent on whether or not the first seven bitscall for a sequence number or not. Each op-code, based on its nature, isfollowed by data in a defined number of bytes. The specific op-codeitself may dictate the number of bytes that follow or alternatively thespecific op-code may dictate that the number of bytes to follow may beextracted from the first byte or several bytes of information thatfollow it. In alternative embodiments, op-codes may have a differentlength, or not be used at all, the message length or message end may bedictated in other ways. Based on the op-code and potentially one or morebytes following it, the receiver knows exactly how many more bytes ofdata to listen for. After receiving those bytes, the receiver may beturned off to conserve power.

For some messages dealing with drug delivery, the data portion of themessage may include a bolus number. The bolus number is similar to thesequence number in that it is incremented by both the implantable deviceand external communication device under controlled conditions so as toreduce the possibility of bolus requests being delivered more than oncewhen duplicate requests may be made as a result of the externalcommunication device failing to receive a confirmation that a previousrequest was received. The bolus number may be a single bit number insome embodiments but in more preferred embodiments it is a multibitnumber (e.g. 2-bit, 4-bit, 7-bit, 1-byte, or 2-bytes) so that it cantake on more than two values thereby making it less likely that an errorwill escape detection due to received and expected numbers erroneouslymatching. The incrementing of the bolus number may occur within theexternal communication device when it receives confirmation that amessage was correctly received and it may be incremented by theimplantable device when it correctly receives a bolus request. As suchwhen a duplicate request for a bolus is received by the implantabledevice it can recognize that the expected and received bolus numbers donot match and that requested bolus is not a new request. As such theimplantable device can respond to the repeated request that the boluswas correctly received and delivered (with out performing a seconddelivery and without incrementing its expectation of what the next bolusnumber will be).

In other embodiments, other incrementing numbers may be used to helpensure that only appropriate operation of the implantable device occurs.For example, incrementing temporary basal rate numbers may be used,and/or separate incrementing numbers may be used for different types ofboluses that might be requested, e.g. immediate boluses and temporaryboluses. In still further alternatives, incrementing message numbers maybe generally used. These message numbers may for example be used on allmessages that have responses associated therewith. Once the receiverconfirms that a message was appropriately received it may increment itsmessage number. Similarly, once the transmitter gets a response to themessage it sent, it may likewise increment its message number.

In the present embodiment, the data portion of the message ends with aone or 2-byte validation or error checking code (its type is dictated bythe op-code included with the message). The preferred error checkingcode of this embodiment is in the form of a cyclic redundancy code(CRC). In other embodiments, the CRC may be replaced with another errorchecking code and/or it may be placed in a different part of the messageor even deleted from the message protocol completely. The op-code mayalso be placed in another part of the message, or deleted in favor ofother techniques that may be used in interpreting the message and fordetermining when the end of the message has been properly received.

In the present embodiment it is preferred that the CRC occur at the endof the message as it simplifies the computational efficiency ofconfirming the validity of the message by the receiver. In alternativeembodiments, where message compilation and transmission occur inparallel, placing the CRC at the end of the message also allows the datato be processed and transmitted in a single pass without a need to havestorage space for the entire message available.

In order to keep power requirements low in a preferred implementation,the external communication device and implantable device attempt tomaintain a common time base, transmissions are set to start at specifiedtimes, and reception windows are set for specified times and lengths. Inthis way, the receiver may remain in a powered down mode most of thetime and can turn on to listen for a potential incoming message at thespecified times for the specified lengths of time. If a message is foundto be incoming, the receiver stays on, otherwise it goes back to sleep(i.e. power down mode).

In the present application, to avoid ambiguities in some portions of thedescription relating to the timing associated with the transmission andreception of messages, the following definitions will be used: (1)“inbound” will generally refer to activities associated with telemetryreception by the medical device, whether implanted or not, or toactivities associated with telemetry transmission by the communicationdevice, (2) “outbound” will generally refer to activities associatedwith the telemetry transmission by the medical device, whether implantedor not, or to activities associated with telemetry reception by thecommunication device.

According to a telemetry timer in the medical device, outboundtransmissions begin at an “outbound transmission start time” andcontinue for an “outbound transmission period” which defines the periodthat the preamble portion of the message is sent which may be though ofin terms of time or in terms of the number of data bits. Similarly,according to a telemetry timer in the communication device, inboundtransmissions begin at an “inbound transmission start time” and continuefor an “inbound transmission period” which defines the period that thepreamble portion of the message is sent which may be thought of in termsof time or in terms of the number of data bits.

Furthermore, according to the telemetry timer in the medical device, thetelemetry reception system of the medical device begins listening formessages at an “inbound listening start time” and continues to listenfor an “inbound listening period” which may be thought of in terms of atime period or a given number of data bits. Similarly, according to theto the telemetry timer in the communication device, the telemetryreception system of the communication device begins listening formessages at an “outbound listening start time” and continues to listenfor an “outbound listening period” which may be thought of in terms of atime period or a given number of data bits. Additionally an “inboundlistening interval” may be thought of as the interval between thesuccessive inbound listening start times while an “outbound listeninginterval” may be thought of as the interval between the successiveoutbound listening start times. Throughout the specification, the abovetiming elements may be referred to in different ways particularly whenit is believed that the intended meaning is clear from the context ofthe description. However, when the precise meaning is required,descriptions will be based on the above definitions so as to removeambiguity.

In the present embodiment time synchronization for telemetrycommunication is maintained using two techniques. The first techniqueperiodically determines the present difference in the concept of time(e.g. second boundaries) as held by the communication device and medicaldevice and the difference is used to reestablish synchronization of thetimers. In the present embodiment, reestablishment occurs on the part ofthe communication device each time it receives a valid communicationfrom the medical device.

The second technique determines a rate of drift that has occurredbetween the concept of time held by the communication device and that ofthe medical device. The determined rate of drift is used in combinationwith a determined lapse in time to estimate how much drift has occurred.This amount of drift is then used in shifting a listening start time ortransmission start time of a first one of the devices to match what isbelieved to be the potential transmission period or listening period ofa second one of the devices. In the present embodiment, the first deviceis the communication device, though in other embodiments it could be themedical device.

In alternative embodiments, variations in drift amounts may be used toextend listening periods and/or transmission periods. They may also beused to force the start of listening or transmission to lead the bestestimate of the transmission or listening start times that that theother device is using. For example, the start of listening ortransmission may be pulled forward by about one-half the amount ofextension applied to the listening or transmission periods,respectively,

Timer periods indicative of reception start times (i.e. listening times)may be generated using a clock signal (i.e. RF one second clock signalin the present embodiment) that is based on a pulse stolen signal (e.g.2¹⁰ Hz signal generated by the system clock ripple counter in thepresent embodiment) plus or minus a value stored in an adjustmentregister (i.e. REG B in the present embodiment which is discussedhereafter). The beginning of a reception period is determined by passingthe RF one-second signal through a start counter and comparing the valueof the start counter to a predefined value stored in a start registerusing a first comparator. The value in the start register dictates howoften reception will automatically be enabled relative to the clocksignal that drives the first counter.

In the implantable device of the present embodiment a programmable butfixed value of 0×1000 is set into REG B which implies an adjustment ofzero to the RF one second clock signal (as will be discussed hereafter).Also in the implantable device of the present embodiment, the value setin the start register is a programmable amount that is set at two fornormal operations and as it is driven by a 1 Hz clock signal, receptionis started every 2 seconds. In the communication device of the presentembodiment, the value used in REG B is varied and the value set in thestart register in combination with the REG B value sets the intervalbetween listening start times to nominally 60 seconds.

When the register value and counter value match, a signal may begenerated by the first comparator to initiate reception. The outputsignal may also be used to clear and enable a period counter that isincremented based on a signal of desired frequency (e.g. about a 8,192Hz signal). The value in the period counter is compared to that in aperiod register using a second comparator. When the values are equal,the second comparator outputs a period signal that resets the value inthe first counter and resets the value in the second counter. The periodsignal may be used to end reception. The resetting of the value in thefirst counter prepares it for the use in establishing the start of nextlistening period. This control technique works because the listeningperiod defined the second counter and second comparator is less than theduration between successive counts of the first counter. In the presentembodiment as the duration is set by a single 8 bit register and theclock driving the counter matches the bit rate for data reception andtransmission, the maximum duration is 256 bit times (e.g. {fraction(1/32)} of a second when using an 8 kHz bit rate). In other embodiments,clock signals other than that corresponding to bit times may be used.

The value placed in the listening period register in combination withthe frequency of the counting dictates the time period between the startlistening and end listening times. The start signal and period signalmay be used in controlling the autonomous listening behavior ofreceiver. In an alternative embodiment, the period signal may be not beused to immediately shut down the receiver but instead an additionalperiod of time may be allotted (e.g. 1 mS) before shut down so as toallow the system to once again check to see if an entire frame syncpattern has been received. This enhancement avoids shutting down thereceiver when a message may have been incoming but in an intermediatestate of having attention preamble already ended but frame sync notfully received at the time the period signal was issued.

In the present embodiment, the time boundaries critical for RFtransmission and reception are the second boundaries and the minuteboundaries. In optimizing the ability of the system to operate at lowpower, the external communication device and the implantable device arecaused to maintain time synchronization. In the present embodiment,dedicated hardware is used to provide enhanced synchronization. In otherembodiments a similar enhancement may be provided in part by softwarethough at a probable increase in power consumption.

In the present embodiment, timer inaccuracy is observed as a differencebetween the timing signals generated in the pulse stolen 8192 Hz clocks(time of day clocks) in the external communication device and theimplantable device. However, if the pulse stolen clocks are running atslightly different frequencies the time-of-day values in the two unitswill slowly diverge. These difference may result from, for example,fluctuation in the oscillation frequency of the crystal oscillator dueto temperature fluctuation or due to slight inaccuracies in the pulsestealing values used. As noted above, the purpose of the timesynchronization operations of the present embodiment are to (1)periodically set the time of day timers in the two devices to the samevalue, and (2) compensate for relative drift between the two timersbetween resettings.

In order to achieve synchronization, the implantable device isconsidered the master and the external communication device synchronizesits time-of-day counter periodically with the time-of-day counter in theimplantable device. In the present embodiment, synchronization isperformed every time a valid message is received from the implantabledevice. As a correction factor, by definition, is not needed in theimplantable device, the RF time synchronization function is disabled bysoftware in the implantable device for both the main and monitorprocessors. In other embodiments, the implantable device instead of thecommunication device may perform the time synchronization function. Instill other embodiments, a modified version of the time synchronizationtechnique may be used to maintain synchronization between the twoprocessor ICs in the implantable device.

Time Synchronization is used to minimize power consumption on theimplantable device side of the system the external communication deviceuses the following hardware to keep track of the passage of time and cantransmit telemetry data bound for the implantable device within thelistening periods used by the implantable device.

FIG. 5 illustrates a block diagram of the various hardware componentsand signals used for time synchronization. Register A (REG A) 102,Register B (REG B) 104, and the Counter C (CNT C) 106 are loadable bythe CPU as illustrated by lines 112, 114, and 116, respectively.Counters A (CNT A) 122 and Counter B (CNT B) 124 both have the same timebase of 8192 Hz as indicated by lines 126 and 128, respectively.

A valid ID signal (IDVALID) 132 is generated when a message for thecommunication is recognized by the hardware. The IDVALID signal 132indicates that the hardware recognized the frame synchronization byteand a 24 bit telemetry ID. As soon as IDVALID is asserted, the value inREG A is loaded into CNT A and CNT A continues to count at the same rateas Counter B but with a predefined starting value, i.e. the valueinserted from REG A.

The value loaded into REG A by the CPU is known. It represents thenumber of bit times that have occurred between the beginning of messagetransmission and the receipt of the telemetry ID. In the presentembodiment, it takes a transmission of 40 bits for the communicationdevice to recognize a valid telemetry ID: (1) 8 bits for the preamble,(2) 8 bits for the frame synchronization byte, and (3) 24 bits for thetelemetry ID. Altogether it takes 40 bits to have the IDVALID signalasserted. The value loaded into REG A is 40*8192/(incoming data rate).For example, if the data rate is 8192 bits/sec, then the value 40 isloaded into REG A and then loaded into CNT A after IDVALID is asserted.Since the implantable device always starts transmitting exactly on theone second boundary based on its own concept of time, i.e. its B countervalue is equal to zero, the IDVALID signal is asserted when theimplantable device's B counter is equal to 40. As such the value loadedinto CNT A of the communication device is initially 40 but thencontinues to increase since CNT A continues counting. After the entiremessage is received, if the CPU determines if the message was valid. Ifvalid, then the value in CNT A of the external communication device isloaded into the CNT B of the external communication device and theimplantable device and external communication device are synchronizedwith respect to time.

In alternative embodiments, the medical device could start itstransmission at other than second boundaries and the communicationdevice could still achieve synchronization if the start time informationwere transmitted with the message so that it could be used by thecommunication device when performing its analysis. In the presentembodiment, the resolution with which synchronization is maintainedcorrelates to the bit rate that is used in data transfer and as suchsynchronization between the two devices is targeted to be maintainedwithin about 1 bit time. In other embodiments, targeted synchronizationresolution may be different from bit time, i.e. it may be greater orsmaller. If smaller, corresponding variations in listening periodsand/or transmission periods may be necessary to accommodate thepotential variance between the timing of the two devices. In still otheralternatives, responsibility for maintaining synchronization could behandled by the medical device or by both devices.

Whenever a valid ID (IDVALID) is recognized by the externalcommunication device the value in CNT B is loaded into the Register C(REG C) 106. The value in REG C may be sent to the CPU as illustrated byline 108. This, along with other information, can then be used todetermine the relative clock error between the implantable device andthe external communication device. The value loaded into REG C minus thevalue in REG A yields the time difference in bit times between theimplantable device's concept of time and the external communicationdevice's concept of time. If the difference is positive, the externalcommunication device's clock is running ahead of the implantabledevice's clock. If the difference is negative, then the externalcommunication device's clock is running behind the implantable device'sclock. Again, using the example above, if the value loaded into REG C is64, and since we know it should have ideally been 40, we know that theexternal communication device has gained 24 counts. This gain in countshas occurred since the last time the implantable device's B counter andthe external communication device's CNT B were synchronized. Taking intoaccount the time interval since the last synchronization occurred, theerror in terms of a rate can be calculated. If the last synchronizationoccurred 5 minutes ago, the external communication device is running 24counts per 5 minutes, or about 10 parts per million, too fast. In orderto avoid inaccuracies in computing the relative error, each new relativeerror is preferably, but not necessarily, averaged with the previouslycomputed error. Also, if the time since the last synchronization is tooshort (e.g. less than 1 to 5 minutes), the error may not be re-computedas it may lack sufficient accuracy. When the drift rate is calculated,it may be used to compute a modified time to start listening for anoutbound message (i.e. outbound from the implantable device) or to starttransmitting an inbound message (i.e. inbound to the implantable device)based on how much time has lapsed since the last communication.

When the external communication device must communicate with theimplantable device, REG B can be used to set a time offset (based on anestimate of drift) to more accurately synchronize thetransmission/reception of the message. An estimated drift value may beloaded into register B. This estimated drift value may be derived, atleast in part, based on the difference between the value stored inregister C and the value stored in register A along with a timedifference between the last two synchronizations (e.g. the last twocommunications), and a time difference between the last synchronization(e.g. the last communication) and the present time. For example, theestimated drift (ED) may be derived from,${ED} = {\frac{{{Reg}\quad C} - {{Reg}\quad A}}{{{Time}\quad 1} - {{Time}\quad 2}}*\left( {{{Time}\quad 0} - {{Time}\quad 1}} \right)}$

Where Reg A and Reg C are the respective values in REG A and REG C, andTime 2, Time 1, and Time 0 are the time of the second to lastcommunication, time of the last communication, and the present time,respectively. A positive value of ED indicates that the externalcommunication device's sense of timing is leading that of theimplantable device while a negative value indicates that the externalcommunication device's sense of time is trailing that of the implantabledevice.

Other ways of deriving the estimated drift value may alternatively beused. As mentioned above, the drift may be determined based on anaverage of a presently determined error rate and one or more previouslydetermined rates. This type of averaging may be unweighted or weighted,based for example on the relative times between successive measurements.In another alternative, the estimate of drift may completely ignore oneor more of the most recent communications and instead be based on thepresent time and the time of an older communication.

Compare circuit 134 compares a value loaded into REG B with the currentvalue in CNT B. When the values match, the compare circuit sends anoutput signal 136 to Register D (REG D) 138 which may be a one-shotflip-flop that produces a single output pulse having a width equal tothat of one cycle (e.g. about {fraction (1/8192)} seconds) of the inputclock signal 142. The output 144 of Register D may be the RF one secondsignal that triggers the onset of various telemetry related activities.

In the present embodiment, it is desired that an upper limit onacceptable estimated drift be set, after which the drift will beconsidered to be excessive and a more extreme technique may be used toreestablish communication. In the present embodiment, if the valueloaded into REG D is within a preset tolerance, or drift limit, (e.g.+/−0.25 seconds) of a nominal transmission or receive time (e.g. a 1second boundary as indicated by CNT B) an RF one second signal is to begenerated.

Confirmation that the value in Register D is within the preset tolerancemay be obtained by comparing selected bit values in Register D topredetermined values for those bits. For example, a bit value of “00010000 0000 0000” may represent a one second boundary in Register D. Thefirst three bits from the left may represent padding so that the valuemay be expressed in a 2-byte manner. The 4^(th) bit from the left mayrepresent a second value, i.e. a value comparable to the 1 Hz clocksignal of the system clock ripple counter. The 5th bit may represent ahalf second value, i.e. a value comparable to the 2 Hz single from theripple counter, and the 6^(th) bit may represent a quarter second value,i.e. a value comparable to the 4 Hz clock signal from the ripplecounter, and so forth. Based on these definitions a value of “0001 11XXXXXX XXXX” is within 0.25 seconds before a second boundary and a valueof “0000 00XX XXXX XXXX” is within 0.25 seconds after the second mark.As such a comparison of the 11th and 12th bit values in register D (oreven to register B) with 00 or 11 will indicate whether the value iswithin the desired range. Of course, other comparisons and selected bitvalues may be used for other preset tolerance amounts. As such, in thisembodiment, prior to an RF one second signal being generated the valueof selected bits in REG D are analyzed to determine if they meet theabove criteria. This analysis may be performed in many ways such as bycomparing the value of the selected bits independently to values forupper and lower limits, or in the case of the above example, by simplyconfirming that the 11th and 12th bits were identical.

In other alternative embodiments excess drift may be determined directlyby comparing a limiting value directly to a value determined for theestimated drift prior to loading any value into REG B. In still otheralternatives, the concept of limiting what drift values may beeliminated. This elimination may come at the expense of transmitting oneor more additional bits of information with messages that indicate oneor more attributes of transmission time (e.g. whether the transmissionstart on an even or odd second boundary or potentially what the secondnumber was. Additional hardware could be added to what was describedabove to handle these alternatives. In other embodiments, portions ofthe synchronization process could be performed by software, such asprocessing of information related to whether the second was even or odd)and then updating registers as appropriate.

As an example, suppose that 2 minutes after receiving thesynchronization message, the communication device needs to transmit amessage to the implantable device. Since the known error is 24 countsper 5 minutes, the external communication device will be about 10 countsfast compared to the implantable device. If in the implantable device, avalue 0×1000 is loaded into the B register, the implantable device willbegin listening and/or transmitting exactly at the one second mark ofthe implantable device. In the external communication device, by loadingthe value (0×1000−0×000A) into the B register, the externalcommunication device will begin receiving and/or transmitting 10 bittimes earlier than it otherwise would and thus as it is anticipated thatthe external communication device's clock is actually 10 bit times aheadof the implantable device's clock the transmission and reception will bereasonably synchronized under the assumption that drift has not changedsignificantly.

As CNT B is updated with the value in CNT A every time a valid messageis received, a current drift amount, though not drift rate, will bereset to zero upon receipt of each message.

Similarly, if the external communication device is programmed orotherwise configured to potentially receive messages from theimplantable device every minute, the value in the B register may beupdated each minute, so that the receiver will be listening at theappropriate times. In the first minute after synchronization, theregister, for example, may be set to 0×1000 minus 0×0005; in the secondminute, 0×1000 minus 0×000A, and so on.

In the present protocol, no more than one message can be received foreach reception window or listening period. In alternative embodiments, a“multiple message op-code” and a “number of messages parameter”, or thelike, may be used such that the receiver knows that it must remain onuntil an indicated number of messages have been received.

As noted above, in a preferred implementation of the present embodiment,telemetry hardware is used to identify the bit sync, frame sync, andtelemetry ID portions of an incoming message as opposed to usingsoftware to interrupt the initial bytes of a potential incoming message.After the hardware confirms that the incoming message is for theparticular receiver, the hardware activates the CPU of the processor ICso that software can aid in receiving, interpreting, and validating themessage. This allows the power consumption of the receiver to remain ata minimum level while waiting for incoming messages to be initiallyscreened. Also as noted above, in a preferred implementation thereceiver only listens for incoming messages at discreet intervals forlimited periods so as to further minimize power consumption associatedwith maintaining communication. As it is preferred that the limitedlistening periods are relatively small compared to the listeningintervals, it is preferred that a reasonable level of timesynchronization be maintained between the transmitter and receiver so asto minimize excess power consumption and user inconvenience associatedwith using extended attention preambles, multiple communicationattempts, or the like, to ensure appropriate information transfer isachieved.

In alternative embodiments, particularly where power consumption is lesscritical, the power of the microprocessor might be utilized to controlthe telemetry hardware during the reception of any or all of thepreamble, frame sync, or telemetry ID portions of the message or mayeven be used to activate the reception hardware at the listening starttime and to deactivate the hardware at the end of the listening periodif it is determined that no message was incoming.

In a preferred time synchronization implementation, the concept of timeat the second and subsecond level is dictated by the implantable device,whereas the concept of time at the minute and hour level is dictated bythe external communication device. Of course, other synchronizationschemes may be alternatively defined.

In the present embodiment, transmissions are allowed to begin only atthe boundaries of seconds as measured by the transmitter's telemetrytimer (taking into account any offsets associated with timesynchronization). Selected boundaries of seconds within each minute areassigned either as a potential outbound transmission start time from theimplantable device to the external communication device or as apotential inbound transmission start time from the externalcommunication device to the implantable device. For example, eachboundary at the beginning of an even second may represent a potentialstart time for inbound transmissions, while one or more odd secondboundaries during each minute may represent potential start times forunsolicited outbound transmissions. A predefined inbound transmissionstart time may be replaced by transmission start time for a solicitedoutbound message as the external communication device is awaiting aresponse to the communication that solicited the response from theimplantable device. In other embodiments, potential transmission timesmay be set to start on something other than boundaries of seconds. Instill other embodiments, the communication device may continue totransmit messages based on inbound transmission start times as theimplantable device may be listening only during predefined inboundlistening periods, while the implantable device may be able to transmitat any time, outside of its normal predefined listening time slots, asthe external communication device may be continuously listening foroutbound communications any time it is not transmitting.

In the present embodiment, depending on the type of message, a 1-byte or2-byte cyclical redundancy code (CRC) follows the data bytes. It ispreferred that the CRC be generally computed using the telemetry ID ofthe message originator (i.e. the telemetry ID of the transmitter). Thisserves as a form of security. If a message with this type of CRC isreceived by an implantable device, the implantable device must haveadvanced knowledge of the telemetry ID of the transmitting externalcommunication device or the implantable device will reject the messagebecause of a CRC error. Similarly the communication device may simplyreject messages that do not originate from its partnered medical device.

A CRC to be included with a message, in the present embodiment, iscalculated based on the successive bytes forming the message andpossibly upon the identity of the transmitter as well. When the CRC iscomputed using the telemetry ID of the message originator, the firstthree bytes used in the calculation are the telemetry ID of theoriginator. The CRC calculation then uses the three bytes of thetelemetry ID of the intended receiver, the 1-byte of op-code, and thenthe remaining bytes of data in the message (with the exception of theCRC itself that is being calculated). When the CRC is not computed withthe message originator's telemetry ID, the CRC is computed based on thebytes of the message starting with the message op-code, and continuingwith the rest of the bytes in the data (with the exception of the CRCitself that is being calculated). Of course, in other embodiments, theCRC calculations may use the telemetry ID of the originator other thanat the beginning of the calculation. In still other embodiments, theop-code may be left out of the CRC calculation. In still otherembodiments, the order in which the components of the messages arecalculated may be changed, though if different from the order presentedin the message itself, recalculation of the CRC by the receiver may notbe able to be performed on the fly as the message is being received asis done in the current embodiment.

In the present embodiment, it is preferred that a precalculated CRCtransmission key and a precalculated CRC reception key are derived andstored so that they do not have to be calculated each time they areneeded. The transmission key is a CRC derived from the byte-by-byteprocessing of the transmitter's three byte telemetry ID followed by thereceiver's three byte telemetry ID. The reception transmission key is aCRC derived from the byte-by-byte processing of the transmitter's threebyte telemetry ID followed by the receiver's three byte telemetry ID.Though these key definitions sound the same it must be remembered thatthe transmitting and receiving roles and devices are reversed. Thesekeys are used as the starting points for deriving the CRC that is to betransmitted with the message and the CRC that is derived upon receipt ofa message, respectively. In other embodiments other keys may be defined.

Further details about CRC generation may be found in (1) the abovereferenced concurrently filed U.S. patent application corresponding toMedical Research Docket No. USP-1079-A, (2) the “CCITT Red Book”, VolumeVIII, published by International Telecommunications Union, Geneva, 1986,Recommendation V.41, “Code-Independent Error Control System”, and (3) “CProgrammer's Guide to Serial Communications”, 2nd Edition, by JoeCampbell, published by SAMS Publishing, Indianapolis, Ind., ISBN0-672-30286-1. In particular chapter 3 of this latter book deals witherrors and error detection including CRCs, while chapter 23 deals withcalculation of CRCs. These books are hereby incorporated by referenceherein as if set forth in full.

In a preferred implementation, the clock in the implantable device isthe master clock in terms of tracking seconds within a minute andsubseconds within a second. The implantable device obtains its conceptof the minute number within an hour and hour within a day from thevalues set in the external communication device which typicallycorrespond to the time of day at the patient's location. The values forsubseconds within a second are preferably transmitted implicitly by theimplantable device to the external communication device based on theimplicit understanding that implantable device transmissions alwaysstart at second boundaries.

More specifically, each time the external communication device receivesa transmission from the implantable device, it uses a combination ofelements to calculate a difference between the external communicationdevice clock and the implantable device clock. These elements include(1) the exact time that a certain portion of the transmission isreceived according to the external communication device clock, (2)knowledge that implantable device message transmission begins a knowntime according to the implantable device's clock, and (3) a known timedifference between that portion of the transmission and the beginning ofthe transmission. These three elements may be used to determine anydifference in time between the clocks and ultimately to resynchronizethe clocks. Of course, in alternative embodiments synchronization may beimplemented in other various ways.

In a preferred implementation, telemetry transmission and reception timeslots begin exactly at one-second boundaries. Some time slots areunassigned while others are assigned as slots for communications thatare inbound to the implantable device. During normal operation each evensecond, relative to the minute mark, is slotted for inboundtransmissions. In a storage mode, the 0, 15, 30, and 45 second marks areslotted for inbound communications. Storage mode is a state of theimplantable device where power consumption is reduced to a minimum levelduring periods of non-use thereby conserving battery power and thusextending the life of the implantable device. The one second mark afterthe roll over of each minute is assigned as a slot for unsolicitedoutbound messages (i.e. messages that are sent without a triggeringmessage from the external communication device). Messages sent from theimplantable device in response to external communication devicecommunications (i.e. solicited messages) are sent out on the nextavailable second mark. In alternative embodiments, it is apparent thatother inbound and outbound slots may be defined.

Since most system communications of the present embodiment originatewith the external communication device, and as a rapid response toprogramming commands is desired for user convenience, it is preferredthat inbound slots be placed relatively close together (e.g. no morethan 15 seconds apart, more preferably no more than 10 seconds apart,and even more preferably no more than 5 seconds apart, and mostpreferably no more than about 2 seconds apart. In order to save batterypower on the external communication device, it is generally preferredthat the system have relative few outbound slots so that the externalcommunication device doesn't consume excessive power when unsolicitedmessages from the implantable device are not often used. In general, itis preferred that there be more predefined inbound time slots per timeperiod than outbound time slots. Of course in alternative embodimentsoutbound time slots may exceed or equal the number of inbound timeslots. When the external communication device sends an inbound messagethat requires a response, the external communication device listens forthe anticipated response from the implantable device that will be sentout on the next one second boundary. If a response is not received in apredefined period of time, the external communication device mayautomatically retransmit the message one or more times prior to alertingthe patient of a failure to communicate.

In the present embodiment, all transmissions both inbound and outbound,and both solicited and unsolicited are sent using the same datatransmission rates and the same carrier frequency. In alternativeembodiments, however, data transmission rates may be varied, and carrierfrequency may be varied. Such variations may be based on predefined timeslot definitions so that both the implantable device and externalcommunication device may properly vary their reception parameters inanticipation of how the other device may attempt to communicate. Forexample, solicited transmissions may occur at a different carrier thanunsolicited transmissions or may occur using a different datatransmission rate. The external communication device may transmit oninbound time slots with a first carrier frequency and first data rate,and the implantable device may transmit on outbound time slots with asecond frequency or second data rate that may be different from thefirst frequency or first data rate. In still further embodiments,transmission reception & frequency may be user selectable ifcommunication problems are excessive in the hope of finding a frequencywith less interference.

To reduce power consumption, it is desirable to have telemetry hardwareoperate only during actual transmission times and during possiblereception times. As such, the hardware, as discussed above, isconfigured and controlled so that this result is achieved. As powerconservation in the implantable device is more critical than powerconservation in the external communication device, this first embodimentplaces the burden associated with synchronization activities andactivities associated with reestablishing synchronization, once it islost, onto the external communication device. This desire to minimizepower drain in the implantable device is balanced with a desire to havethe implantable device respond quickly to commands transmitted by theexternal communication device. Once a command is issued by the externalcommunication device, it is preferred, for user/patient convenience,that the implantable device receive and acknowledge the command asquickly as possible. To this end, the implantable device is providedwith closely spaced reception slots (i.e. inbound listening intervals,e.g. every 2 seconds) so that communication can occur with asufficiently fast response. Each inbound listening period, however, isof very short duration so that power consumption in the implantabledevice is minimized.

The duration of each inbound listening period is preferably not so smallthat slight variations in synchronization cause lost of reception, whichwould cause a delay in communication, as well as potentially causingextra power consumption in order to reestablish communication as thereception hardware may be forced to remain on for extended periods oftime due to the reception of lengthy attention preambles. As such, inthe present embodiment the reception time slots are turned on for aninitial period of about 2-8 milliseconds (e.g. 4 milliseconds) whileusing an 8 kHz data transmission rate with a minimum number of 8-bittransitions necessary for establishing bit synchronization.

In alternative embodiments longer or shorter windows may be used.Relative to the incoming bit rate, it is preferred that the windowremain open in the range of about one and one-half to four times theperiod necessary to establish bit sync and receive a complete frame syncsignal.

In other alternative embodiments, if attention preamble is sent, thewindow may be opened only for a period necessary to establish receipt ofthe attention preamble and thereafter, frame sync and a valid telemetryID may be looked for. In this alternative, to enhance likelihood ofreception, the transmitter preferably does not begin transmission atwhat it believes is the most likely time that the receiver beginslistening, but instead begins transmission at a somewhat earlier timewith an attention preamble of sufficient length to cover or at leastsufficiently overlap the anticipated listening period.

In the present embodiment, the implantable device always starts atransmission exactly at (an outbound transmission start time whichcorresponds to a second boundary) according to its own clock. Theexternal communication device may activate its receiver at what itbelieves is the implantable device's outbound transmission start timebased on use of any synchronization parameters established inconjunction with the previous communication(s). The externalcommunication device may leave its reception window open for apredefined minimum period of time or alternatively it may adjust thelistening period based on one or more parameters. The receiver may useone or more additional parameters to adjust the opening of the receptionwindow to somewhat earlier than what it believes the actual start of thepotential transmission is to be. This early opening of the receptionwindow may be based on an anticipation that a certain amount ofincreasing uncertainty exists in the validity of the previouslyestablished synchronization and associated previously established driftparameters. In other words, this may be done in recognition that thereis a tolerance around which synchronization may be drifting. Suchadditional parameters may also be used to lengthen the reception windowbeyond a predefined initial listening period.

In this embodiment, the implantable device always turns on its receiverexactly at the beginning of an inbound reception time slot. As such, ifthe external communication device has a message to transmit to theimplantable device during that reception time slot, the externalcommunication device may start transmitting at what it believes is thebeginning of the time slot based on an estimated amount of drift thatmay have occurred. Alternatively, it may begin transmitting somewhatahead of its best estimate as to when the time slot will open, inanticipation that there is some degree of uncertainty in the actualamount of drift that has occurred between its measure of time and thatof the Implantable Device. In this regard, the external communicationdevice may use an extended preamble, possibly of the standard pattern ifnot extended too long, but more preferably of the attention pattern sothe chance of establishing communication is increased due to thereceiver's attribute of having its attention held (i.e. receptionhardware retained in an active state) by a communication that consistsof the attention preamble pattern. The parameter used in causing thewindow to open early may be a fixed parameter, or a parameter that isbased, at least in part, on the time difference between the present timeand the time of last establishing synchronization and possibly based onan estimate of maximum likely drift rate or based on an actual amount ofdrift experienced between the last two communications or between severalcommunication or associated with an amount or amounts of driftexperienced during approximately the same time periods during one ormore previous days. Similarly, the parameter used to extend the lengthof the standard preamble or attention preamble, or even to selectbetween them, may be a fixed parameter, a parameter that is based, atleast in part, on the time difference between the present time and thetime of last establishing synchronization or a parameter with adifferent basis.

If it is determined that resynchronization is needed, the externalcommunication device may establish re-synchronization in one of severalways. The external communication device may transmit a message with anextended preamble consisting of the attention preamble. This process maybe done as a single step or it may be done in multiple steps. In thesingle step process, the attention preamble is set to a length of timeequal to or somewhat greater than the length of time between inboundlistening intervals. This message is preferably a sync message as willbe discussed hereafter though it may be also be a different message.After transmission of the message, the external communication deviceleaves its receiver open for at least about 1-2 seconds in anticipationof the implantable device sending an outbound response. The timing ofthe sync response message, as well as its content, will provide theinformation necessary to reestablish synchronization.

The sync message is preferred over other messages because other messagesmay not carry as much information about timing between the implantabledevice and the external communication device as is carried by the syncmessage. For example, all response messages may be used to reestablishsynchronization of the second boundaries, but not all messagesnecessarily carry sufficient information to reestablish even versus oddsecond boundaries or information necessary to reestablish one-minuteboundaries.

In one variation of this one step process, the external communicationdevice begins transmission of the message somewhat after its bestestimate (if it has one) as to when the reception window on theimplantable device will be closing. In this variation, it is hoped thatthe implantable device's receiver will open its reception window towardsthe end of transmission of the attention preamble, as opposed to towardthe beginning of transmission, so that power consumption by theimplantable device is minimized.

One potential multi-step process is similar to the one step processdiscussed above, but the first one or more attempts to establishsynchronization use an attention preamble that is shorter than theinbound listening interval. In this regard, if the transmission catchesthe window, the receiver of the implantable device may be held open fora shorter period of time than that resulting from the one step processand thus a power savings in the implantable device may be achieved.However, if the transmission is not received, one or more subsequentmessages will need to be sent, with the associated inconvenience of anextra time delay. In this process, the first message is preferablycentered around the external communication device's best estimate as toinbound listening period. If communication and synchronization are notreestablished in response to the first message, one or more subsequentmessages may be transmitted with longer attention preambles that stillmay be shorter than the interval between inbound time slots, equal toit, or even greater than it. In any event, if communication andsynchronization are not reestablished using the previous attempts, afinal message will be sent with an attention preamble of length equal toor greater than the inbound listening interval. If communication hasn'tbeen reestablished based on transmitting attention preamble for a periodof time equal to or somewhat greater than the normal operation inboundlistening interval, it may be appropriate to send an attention preamblefor a time period equal to or somewhat greater than the storage modeinbound listening interval as the system may have inadvertently beenshifted to that mode. If communication is still not established, thepatient may be alerted to the problem so that he/she may reposition theexternal communication device relative to the implantable device, go toa different location where electromagnetic interference may be reduced,or otherwise seek assistance in addressing the problem.

As a second example of a potential multistep synchronization process thelength of the attention preamble may not be increased beyond thatselected for the first attempt, instead if multiple attempts are needed,the start time of transmission may be shifted such that the entire setof messages, if required to be sent, will cover all possible portions ofthe inbound listening interval by covering a different portion of eachinterval in a series of intervals.

As a further alternative, if unsolicited communications are outboundfrom the implantable device on a periodic basis, the externalcommunication device may simply open its reception window for the entireinterval between at least two of the successive periodic outboundcommunications so the message known to be transmitted sometime duringthe interval will be received assuming that the devices are withintelemetry range and other problems are not present such thatsynchronization may be reestablished.

Some messages may be transmitted without expecting a response, in whichcase the sender will not know whether they were correctly received(non-response transactions). Other messages may require a response. If aresponse to these messages is not received, the transmitter will respondto the failure by repeating transmission of the message. After apredefined number of transmission attempts without a response, themessage may be declared undeliverable, and the patient may be alerted tothe problem. In the present embodiment, status messages do not require aresponse.

All messages (with the exception of the link message and the interrogatemessage) that require a response and trigger an action in the receiver,and all responses to such messages, are transmitted with a sequencenumber. In the present embodiment, that sequence number is a single bitthat identifies the sequence of messages. As such, this sequence numberis toggled between its two possible states “1” and “0”, by thetransmitter each time a message is sent and the appropriate response(including the sequence number) is received. The receiver toggles itsconcept of what the sequence number should be when it receives a validmessage with the sequence number that it is next expecting. If itreceives a message with a sequence number it is not expecting, it sendsa response indicating that the message was received but does not actupon the content in the message. In alternative embodiments, thesequence numbering may be removed or enhanced to include more than onebit. The sequence number is used to ensure that a given message is onlyacted upon once, though the message may be received multiple times andmultiple responses sent out. This situation may occur when the senderdoes not receive the response and then automatically resends the messageone or more times. If a response is not received after one or moreattempted retransmissions, the synchronization process is attempted. Ifthat fails, the patient is alerted to the condition so that subsequentsteps may be taken. In any event, once communication is reestablished,the message is resent and an appropriate response looked for. If theoriginal message was not received in the original transmission attempts,and was only received in the last transmission attempt, and it dealtwith an insulin delivery issue that was not longer applicable, thedelivery could be canceled by going into a suspend mode or by takingother steps in a timely manner. Suspend mode is an operational state ofthe implantable device where insulin delivery is reduced to a medicallyinsignificant level.

If a received message requires a response, the recipient responds duringthe next available transmission period. If a received message has anincorrect CRC, it is ignored. In the present embodiment, the sender of amessages waits a predetermined period of time for the anticipatedresponse message and if it does not receive the response as expected, ittakes the appropriate course of action as noted above.

The user may need to change the time defined in the externalcommunication device. This may result from changes when travelingbetween time zones, due to annual shifts in time, as well as due toslight errors in tracking time. In the present embodiment, the externalcommunication device keeps track of minutes, hours, and days based onthe operation of its clock and any updates from a user. The externalcommunication device receives it concept of seconds within a minute fromthat found in the implantable device and as such does not allow userinput to update a second value. The external communication device doesnot track seconds within minutes. When the user changes the time on theexternal communication device, an appropriate message is transmitted tothe implantable device so that it may adapt to the new time of day. Thisis done because certain automatic delivery regimes (e.g. basal rateprofiles) are based on the time of day. In the present embodiment,delivery is not automatically changed between various days of the weekor month and as such the implantable device has no need of tracking thisinformation. However, if in alternative embodiments day sensitivedelivery routines are implemented in an automated manner then theexternal communication device could be programmed to pass thisinformation to the implantable device which may be programmed to acceptand use it. If it is found desirable for the communication device totrack seconds, in an alternative embodiment, the medical device couldobtain its concept of seconds from the communication device.

In some embodiments, software may be downloaded from the externalcommunication device to the implantable device. The downloading ofsoftware may include the downloading of executable software as well asthe downloading of data structures that may be used by the executablesoftware.

In the present embodiment, a specific external communication device isconfigured/programmed to communicate substantively with only onespecific implantable device, that is in turn configured/programmed tocommunicate substantively with only the same specific externalcommunication device. An external communication device is capable ofretaining the telemetry ID of exactly one implantable device at a timeand an implantable device is capable of retaining the telemetry ID ofexactly one external communication device at a time. A small amount ofnon-substantive communication (i.e. communication that does not impactinsulin delivery) can occur between external communication devices andimplantable devices that are not linked (i.e. partnered or married) toone another (i.e. provided with each others telemetry IDs). Onlycommunications between linked devices are used in the timesynchronization process.

In the present embodiment, many different types of messages andresponses thereto can be written into the programs that control theimplantable device and the external communication device according tothe protocol features set forth above These messages may be used for anumber of different purposes. For example, (1) they may be system levelmessages that are used for testing devices, for resetting devices, orfor establishing relationships between implantable devices and externalcommunication devices, (2) they may be alarm messages that are used toconvey alarm conditions or to clear alarm conditions, (3) they may bemiscellaneous messages that set various parameters or perform variousread operations, (4) they may be delivery messages that set deliveryamounts, read delivery status, or set parameters such as concentrationand pump stroke volume that may be required to appropriately controldelivery of the drug, (5) they may be data log messages that set datalog boundaries, read boundaries, or clear data logs, boundaries or readinformation from various data logs or supply information to those datalogs, (5) they may be refill messages that are related to amounts ofmaterial that are added to the reservoir periodically, (7) they may becompound messages that perform more than one function, or (8) they maybe error messages that request error condition status or supply errorcondition status. In other embodiments, messages may be classified indifferent ways.

Various the features of the above embodiment and its alternativesprovide enhanced accuracy of timers, ability to transmit and receivemessages in target time periods, ability to accurately synchronize thetime periods so that communication can occur with little inconvenienceto the user and with little waste of power, ability to recover from aloss of synchronization in an power and/or time efficient manner, and/orability to reduce power consumption. These improvement provide morerobust, effective, reliable, and safe operation of an implantablemedical device and more generically for an ambulatory medical device.

While the above embodiment has primarily been concerned with animplantable infusion pump that dispenses insulin using a piston typepump mechanism, the telemetry and timing features disclosed herein maybe used in other ambulatory devices such as implantable pacemakers,defibrillators, other implantable tissue stimulators, implantablephysiologic sensors such as electrochemical oxygen sensors, peroxidesensors, or enzymatic sensors such as glucose sensors, externallycarried infusion pumps, implantable infusion pumps that use otherpumping mechanisms or simply used excess pressure and controlled flowelements to infuse various medications and drugs such as analgesics,drugs for treating AIDS, drugs for treating psychological disorders andthe like. For example, the telemetry features presented above may beused with an external infusion pump that may or may not have a built indisplay and keypad but is equipped with a telemetry system that cancommunicate with a physically separated communication device so that thepump need not be accessed in order to provide commands to it and receivedata from it.

In these various alternatives, the physical, electronic, and programmedfeatures of the communication device and implantable device may havedifferent components and features than presented above for theimplantable pump system so that their desired medical functionality andsafety requirements are achieved and such that appropriate control andfeedback is provided between the medical device and its communicationdevice.

In other alternative embodiments the medical device may include twomedical devices such as an implantable pump and an implantable sensor.The pump may dispense a drug whose physiological impact on the body(e.g. analgesic impact) is ascertained by the sensor or alternativelythe sensor may supply a physiological reading that indicates a need forinfusion of the drug. The pump may operate in a closed loop manner withthe sensor or it may operate in an open loop manner where the patient isrequired to interpret sensor output information and is required to issueappropriate infusion commands to the pump. For example, in the case of adiabetic patient, the drug may be insulin and the sensor may detectglucose level.

In other alternative embodiments two medical devices may be implantedadjacent one another or at an extended distance from one another. If notplaced in physical contact with one another, a lead may be used toprovide power conduction from one device to the other and also be usedto conduct communication signals between the devices. Alternatively,each device may include at least one telemetry system that allows directcommunication between each or allows indirect communication to occur viathe external communication device or other external device. Each devicemay be supplied with its own power supply. Depending on thecommunication requirements each device may use two way communication(i.e. both outbound and inbound communication) or allow only one waycommunication (i.e. outbound communication or possibly inboundcommunication).

In other alternatives, both the medical device and the communicationdevice may be external devices (e.g. an external pump and an external RFtelemetry based communication device). In still further alternatives, afirst type of medical device may be implanted (e.g. an infusion pump ora sensor) while a second medical device may be external (e.g. theopposite of a sensor or an infusion pump). Where at least one of themedical devices is external, it may also function as the communicationdevice for the other medical device in which case it may possess adisplay for providing information to the patient and a keypad forallowing entry of commands for issuance to the implantable device aswell as for direct use by itself. Even if at least one of the medicaldevices is external, it may be inconvenient to access that device wheninformation is needed or commands must be given, as such an external,non-medical communication device may be supplied that has informationoutput (e.g. display) capabilities and input (e.g. keypad) capabilities.If a separate communication device is provided, the external medicaldevice may or may not have display and input capabilities.

The telemetry features presented above may be used with various forms ofdistant communication (e.g. between the implantable device and otherexternal devices or between the external communication device and otherexternal devices). For example communication may occur via variouselectromagnetic links like IR, optical links, longer or shorterwavelength RF, audio links, ultrasonic links, acoustic links, inductivelinks, and the like. Various telemetry systems may be used. Telemetrysystems may be of the analog type, digital type, or mixed.

The various telemetry and timing features presented above may be used invarious combinations be used separately to enhance communicationsbetween ambulatory medical devices and communication devices and/orcontrollers associated therewith.

In other embodiments two independent processors may be used that operatefrom a single timing chain. In these alternatives, it is preferable thatat least one of the timing signals (e.g. one of the lower frequencytimers) be monitored by an independently timed watchdog circuit toreduce the risk of timing problems going undetected.

In still additional embodiments, an implantable glucose sensor may beused in conjunction with an implantable insulin pump to provide feedbackto the patient or physician on the effectiveness of the insulin deliverysystem. The patient could use the feedback to assist in making insulindelivery decisions in an open loop manner. Alternatively, the operationof the pump could be tied to the sensor output in a more or less closedloop manner to give a more automated character to system operation.Insulin may be infused without any user intervention, withoutpre-delivery information, and even without direct post deliveryfeedback. In a less automated closed loop system, drug infusionrecommendations could be derived by the system and presented to the userbefore delivery or the system could require user acknowledgment prior toproceeding with delivery for amounts or rates exceed a predefined limit.The implantable sensor may have its own power supply or may receivepower from the control circuitry provided within the pump housingthrough a physical lead that connects them. Power may be suppliedthrough one or more independent leads or alternatively may betransferred over one or more data lines through the communicationsignals themselves. Communication may be exchanged in various waysincluding, for example, via galvanic leads, RF telemetry, fiber optics,and the like, and may be of digital, analog, or combined form. Thesensor system may include a plurality of sensor elements which mightallow continued glucose data to be supplied even though some portion ofthe sensors stop operating, lose calibration or produce questionablereadings. The most preferred sensors would include electronic processingcapability in the form of an integrated circuit mounted in or forming apart of a housing for the sensor. This configuration has the advantageof allowing digital communications between the physical sensor and anyseparated electronic control module.

Further teachings concerning implantable sensors and implantable sensorsystems are found in a number of patents issued to D. A. Gough,including (1) U.S. Pat. No. 4,484,987, entitled “Method And MembraneApplicable To Implantable Sensor”; (2) U.S. Pat. No. 4,627,906, entitled“Electrochemical Sensor Having Improved Stability”; (3) U.S. Pat. No.4,671,288, entitled “Electrochemical Cell Sensor For ContinuousShort-Term Use In Tissues And Blood”; (4) U.S. Pat. No. 4,703,756,entitled “Complete Glucose Monitoring System With An ImplantableTelemetered Sensor Module”; and (5) U.S. Pat. No. 4,781,798, entitled“Transparent Multi-Oxygen Sensor Array And Method Of Using Same”. Eachof these patents is incorporated herein by reference as if set forth infull.

Still further teachings concerning implantable sensors and sensorsystems are found in a number of patents issued to J. H. Schulman, etal., including (1) U.S. Pat. No. 5,497,772, entitled “Glucose MonitoringSystem”; (2) U.S. Pat. No. 5,651,767, entitled “Replaceable CatheterSystem for Physiological Sensors, Stimulating Electrodes and/orImplantable Fluid Delivery Systems”; (3) U.S. Pat. No. 5,750,926,entitled “Hermetically Sealed Electrical Feedthrough For Use WithImplantable Electronic Devices”; (4) U.S. Pat. No. 6,043,437, entitled“Alumina Insulation for Coating Implantable Components and OtherMicrominiature Devices”; (5) U.S. Pat. No. 6,088,608, entitled“Implantable Sensor and Integrity Test Therefor”; and (6) U.S. Pat. No.6,119,028, entitled “Implantable Enzyme-Based Monitoring Systems HavingImproved Longevity Due to Improved Exterior Surfaces”. Each of thesepatents is incorporated herein by reference as if set forth in full.

Additional further teachings concerning implantable sensors and sensorsystems are found in (1) U.S. Pat. No. 5,917,346, issued to J. C. Gord,et al., and entitled “Low power current-to-frequency converter”; (2)U.S. Pat. No. 5,999,848, issued to J. C. Gord, and entitled “DaisyChainable Sensors for Implantation in Living Tissue”; (3) U.S. Pat. No.5,999,849, issued to L. D. Canfield, et al., and entitled “Low PowerRectifier Circuit for Implantable Medical Devices”; and (4) U.S. Pat.No. 6,081,736, issued to M. S. Colvin, et al., and entitled “ImplantableEnzyme-Based Monitoring Systems Adapted for Long Term Use”. Each ofthese patents is incorporated herein by reference as if set forth infull.

Further teachings concerning implantable infusion pumps are found in anumber of patents by R. E. Fischell, including (1) U.S. Pat. No.4,373,527, entitled “Implantable, Programmable Medication InfusionSystem”; (2) U.S. Pat. No. 4,494,950, entitled “Infusion Device Intendedfor Implantation in a Living Body”; (3) U.S. Pat. No. 4,525,165,entitled “Fluid Handling System for Medication Infusion System”; (4)U.S. Pat. No. 4,573,994, entitled “Refillable Medication InfusionApparatus”; (5) U.S. Pat. No. 4,594,058, entitled “Single ValveDiaphragm Pump with Decreased Sensitivity to Ambient Condition”; (6)U.S. Pat. No. 4,619,653, entitled “Apparatus For Detecting At Least OnePredetermined Condition And Providing An Informational Signal InResponse Thereto In A Medication Infusion System”; (7) U.S. Pat. No.4,661,097, entitled “Method for Clearing a Gas Bubble From a PositiveDisplacement Pump Contained Within a Fluid Dispensing System”; (8) U.S.Pat. No. 4,731,051, entitled “Programmable Control Means for ProvidingSafe and Controlled Medication Infusion”; and (9) U.S. Pat. No.4,784,645, entitled, “Apparatus For Detecting A Condition Of AMedication Infusion System And Providing An Informational Signal InResponse Thereto”. Each of these patents is incorporated herein byreference as if set forth in full.

Still further teachings concerning infusion pumps are found in a numberof patents by Franetzki, including (1) U.S. Pat. No. 4,191,181, entitled“Apparatus For Infusion of Liquids”, (2) U.S. Pat. No. 4,217,894,entitled “Apparatus for Supplying Medication to the Human or AnimalBody”; (3) U.S. Pat. No. 4,270,532, entitled “Device for thePre-programmable Infusion of Liquids”; (4) U.S. Pat. No. 4,282,872,entitled “Device for the Pre-programmable Infusion of Liquids”, U.S.Pat. No. 4,373,527, entitled “Implantable, Programmable MedicationInfusion System”; (5) U.S. Pat. No. 4,511,355, entitled “Plural ModuleMedication Delivery System”, (6) U.S. Pat. No. 4,559,037, entitled“Device for the Pre-programmable Infusion of Liquids”; (7) U.S. Pat. No.4,776,842, entitled “Device for the Administration of Medications”. Eachof these patents is incorporated herein by reference as if set forth infull.

Teachings concerning tissue stimulators are found in a number of patentsby J. H. Schulman, including (1) U.S. Pat. No. 5,193,539, entitled“Implantable microstimulator”; (2) U.S. Pat. No. 5,193,540; entitled“Structure and Method of Manufacture of an Implantable Microstimulator”;and (3) U.S. Pat. No. 5,358,514, entitled “Implantable Microdevices withSelf Attaching Electrodes”. Further teachings are also found in (1) U.S.Pat. No. 5,957,958, by Loeb et al., entitled “Implantable nerve ormuscle stimulator e.g. a cochlear prosthesis”, in (2) U.S. Pat. No.5,571,148, by G. E. Loeb, et al., entitled “Implantable MultichannelStimulator”; and in (3) PCT Publication No. WO 00/74751, by A. E. Mann,and entitled “Method and Apparatus for Infusing Liquids Using a ChemicalReaction in an Implanted Infusion Device”. Each of these publications isincorporated herein by reference as if set forth in full.

The control of an implantable sensor could be provided through thefunctionality of one or both Processor ICs. One Processor IC couldsupply power and/or control signals to the sensor(s) and receive databack from the sensor, while the other processor could monitor theactivity to ensure that sensor activity meets certain predefinedguidelines.

In other embodiments, the External Communication Device of the firstembodiment could be functionally linked to an external glucose sensorsystem such as the continuous glucose monitoring system (CGMS) offeredby Minimed Inc. of Northridge, Calif. The link may be established, forexample, through a physical lead or by RF telemetry.

In other embodiments other implantable, or external, sensor systems thatmeasure something other than glucose could also be functionally coupledto the implantable device either to receive power and/or to providedata. Other such sensors might include oxygen sensors, peroxide sensors,pulse rate sensors, temperature sensors, accelerometers, and the like.

In still other alternative embodiments, the electronic control system ofthe first embodiment could be configured to control one or moreimplantable sensors or electrical stimulators with or without infusionfunctionality incorporated into the implantable device.

Further embodiments will be apparent to those of skill in the art uponreview of the disclosure provided herein. Still further embodiments maybe derived from the teachings set forth explicitly herein in combinationwith the teachings found in the various patent applications.

While the description herein sets forth particular embodiments, it isbelieved that those of skill in the art will recognize many variationsto the presented embodiments based on the teachings herein, as such itis believed that many additional modifications may be made withoutdeparting from the spirit of the teachings herein. The accompanyingclaims are intended to cover such modifications as would fall within thetrue scope and spirit of the present invention.

The disclosed embodiments are therefore to be considered as illustrativeand not necessarily restrictive, the scope of the invention beingindicated by the appended claims, rather than the foregoing description,and all changes which come within the meaning and range of equivalencyof the claims are therefore intended to be embraced therein.

We claim:
 1. A medical system, comprising: a) an ambulatory medicaldevice (MD) comprising MD electronic control circuitry that furthercomprises at least one MD telemetry system and at least one MD processorthat controls, at least in part, operation of the MD telemetry systemand operation of the medical device, wherein the medical device isconfigured to provide a treatment to a body of a patient or to monitor aselected state of the body; and b) a communication device (CD)comprising CD electronic control circuitry that further comprises atleast one CD telemetry system and at least one CD processor thatcontrols, at least in part, operation of the CD telemetry system andoperation of the communication device, wherein the CD telemetry systemsends messages to or receives messages from the MD telemetry system,wherein at least one of the communication device or the medical devicesets a preamble length, for at least some messages, as a function of atleast the difference between a present time and a time of a previouscommunication.
 2. The system of claim 1 wherein a first portion of theMD telemetry system is incorporated into the MD processor and a secondportion of the MD telemetry system is external to the MD processor, orwherein a first portion of the CD telemetry system is incorporated intothe CD processor and a second portion of the CD telemetry system isexternal to the CD processor.
 3. The system of claim 2 wherein (1) theMD electronic control circuitry comprises at least one external MDfunctional module, other than the second portion of the MD telemetrysystem, that is external to the MD processor, (2) the CD electroniccontrol circuitry comprises at least one external CD functional module,other than the second portion of the CD telemetry system, that isexternal to the CD processor, (3) the MD processor comprises an internalMD CPU and at least one other internal MD functional module, or (4) theCD processor comprises an internal CD CPU and at least one otherinternal CD functional module.
 4. The system of claim 1 wherein themedical device comprises at least one of (1) an implantable infusionpump for selectively dispensing a selected drug, (2) an implantableinfusion pump for selectively dispensing insulin, (3) an implantablesensor for sensing a selected state of the body, (4) an implantablesensor for sensing glucose level, or (5) an implantable electrode forselectively stimulating a portion of the body of the patient.
 5. Themedical system, of claim 1, wherein the medical device sends outboundmessages to the communication device and the communication devicereceives outbound messages from the medical device, wherein the medicaldevice receives inbound messages from the communication device and thecommunication device sends inbound messages to the medical device,wherein the medical device listens for inbound messages beginning at aninbound listening start time and continuing for an inbound listeningperiod, wherein the communication device listens for outbound messagesbeginning at an outbound listening start time and continuing for anoutbound listening period, wherein the medical device transmits outboundmessages beginning at an outbound transmission start time and continuestransmission of a selected portion of the outbound messages for anoutbound transmission period, wherein the communication device transmitsinbound messages beginning at an inbound transmission start time andcontinues transmission of a selected portion of the inbound messages foran inbound transmission period, wherein an interval exists betweensuccessive inbound listening periods, wherein an interval exists betweensuccessive outbound listening periods, wherein at least a selected oneof (1) or (2) occurs: (1) at least one of the inbound transmissionperiod or the outbound transmission period is extended after a failureto communicate occurs; or (2) at least one of the inbound transmissionstart times or outbound transmission start times undergoes a shiftrelative to an anticipated inbound listening start time or ananticipated outbound listening start time, respectively; and whereinafter one or more extensions and/or one or more shifts, all portions ofthe interval between successive inbound or outbound listening periodswould be broadcast to during inbound transmission periods or outboundtransmission periods, respectively.
 6. The system of claim 5 wherein afirst portion of the MD telemetry system is incorporated into the MDprocessor and a second portion of the MD telemetry system is external tothe MD processor, or wherein a first portion of the CD telemetry systemis incorporated into the CD processor and a second portion of the CDtelemetry system is external to the CD processor.
 7. The system of claim6 wherein (1) the MD electronic control circuitry comprises at least oneexternal MD functional module, other than the second portion of the MDtelemetry system, that is external to the MD processor, (2) the CDelectronic control circuitry comprises at least one external CDfunctional module, other than the second portion of the CD telemetrysystem, that is external to the CD processor, (3) the MD processorcomprises an internal MD CPU and at least one other internal MDfunctional module, or (4) the CD processor comprises an internal CD CPUand at least one other internal CD functional module.
 8. The system ofclaim 5 wherein (1) the MD electronic control circuitry comprises atleast one external MD functional module, other than the second portionof the MD telemetry system, that is external to the MD processor, (2)the CD electronic control circuitry comprises at least one external CDfunctional module, other than the second portion of the CD telemetrysystem, that is external to the CD processor, (3) the MD processorcomprises an internal MD CPU and at least one other internal MDfunctional module, or (4) the CD processor comprises an internal CD CPUand at least one other internal CD functional module.
 9. The system ofclaim 5 wherein the medical device comprises at least one of (1) animplantable infusion pump for selectively dispensing a selected drug,(2) an implantable infusion pump for selectively dispensing insulin, (3)an implantable sensor for sensing a selected state of the body, (4) animplantable sensor for sensing glucose level, or (5) an implantableelectrode for selectively stimulating a portion of the body of thepatient.
 10. The system of claim 1, wherein the preamble length isextended, based on the difference between a present time and a time of aprevious communication.
 11. The system of claim 1, wherein a preamblefor at least some messages comprises a repeating pattern of bits. 12.The system of claim 1, wherein a preamble for at least some messagescomprises an alternating pattern of ones and zeros.
 13. The system ofclaim 1, wherein a preamble for messages being sent from the CDtelemetry system to the MD telemetry system have a different length thana preamble for messages being received by the DC telemetry system fromthe MD telemetry system.
 14. The system of claim 1, wherein saidmessages comprises a preamble and data.
 15. The system of claim 14,wherein a preamble for at least some messages comprises an attentionpreamble pattern of bits and wherein a receiver of at least one of theCD telemetry system and the MD telemetry system operates to continue totrack received bits of a message, in response to receiving the attentionpreamble pattern of bits for the message.
 16. The system of claim 1,wherein a preamble for at least some messages comprises an attentionpreamble pattern of bits and wherein a receiver of at least one of theCD telemetry system and the MD telemetry system operates to continue totrack received bits of a message, in response to receiving the attentionpreamble pattern of bits for the message.